First, I just going ask the goal first:
Is it to "bring GT into Xcom2" or "turning Xcom2 into GT"??

The thing that makes GT differs from Xcom2 in combat stuff often tied to the map and enemy numbers:
Xcom2 is known for larger map, enemy pods separated far and comes in small size number (when compared to your squad size) but quality except The Lost. Trying 1v2 late-game mob could get even your high level soldier killed if not properly done.

GT instead often gives you smaller map where enemies could even reach the other side of the map in 2-3 turns moves except few. Thus enemy pods are tight and mobs number are high when compared to your small 4 member unit. But, 1-hit kill mobs pretty much existed often and becomes a stepstone for plethora of "On kill..." combo.

You will often find one of your unit facing 1 vs 3 enemies in GT (either all just 1-action kill mob like The Lost in WotC or elites mixed in) while in Xcom it is about ganking up a pod 2:1 once the conceal is broken. Which is why there are so many AP gain or free action in GT.
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Anyway, the long feedback on the classes. As per what I said before, depending on your goal then things may got changed/ignored.

- You should recheck all "upgradeable skills" required ability. For example:
* Support's stim, empower, adrenaline, teamwork
* Scout's enhanced exertion
* Vanguard's Rally to Spur
=> All these skills' upgraded version can be learned and used without having the lower level. While Stim requires Stim I to enable the revival protocol, you can skip Stim II effect if you don't feel like need to and goes straight for Stim III.

- All scout's melee related skill should ONLY interact with melee weapons, you need to put up that requirement like on blademaster or else the game may crash when coming with other mods. Right now, it is funny how you can equip a pistol into utility slot and do a Scout's Slice and Dice with it

- Probably need to give all classes the Skirmisher's marauder passive. For example, Scout has bloodrush ability which a buff on-kill, but this class has no follow-up move after any attack (overdrive, serial, reaper, hit and run, double tap, etc). So after this class killed someone/something, the turn pretty much ended. So the blood rush only gives effect for only the next turn?

- Distraction 1 pretty much a wasted or suicide since the vanilla AI sometimes ignores hit chance and just goes for weaker health unit if it is on certain range. That is unless the "balancedly spread out AI" mod applied. Also to note, in Xcom2, you practically do not want your unit to get hurt due to the wound and will loss system. Perhaps the damage reduction should be applied earlier (eg 25% at level 1 > 50% level 2) instead zero DR

-Enhanced Finisher has "Crit Boni" in the description ??

- Where is Inspiration 2 ??

Added long texts
Stuffs you should consider if the plan goes to "converting XCom into GT"

1. Everyone can attack (shoot, melee, grenade, etc) or move multiple times, in any order, as long there is still AP available. Also there is no turn ending skill other than the overwatch in GT (or as far as I remember). Rather than giving them a Skirmisher's Marauder, it is easier to just give a "permanent / passive" Overdrive from Spark (with AdaptiveAim along).

2. Everyone has a grenade. Can easily be done by borrowing the grenade pocket from other perks mod. But again, that is suboptimal. Instead, I recommend you to bring in a custom grenade / utility launcher instead, with cooldown instead of charges. You can take example of Andromedon's Acid launcher for this. You may also assign the "plant grenade" to this same "launcher".

Take example of Wraith Suit (LightPoweredArmorMk2) or Gauntlet which has two perks attached to it for LW2, except with cooldown instead charges. Then create a tier for this launcher to replicate the tiered grenade from GT (along with alternative if you want to have stim grenade). You can disable native grenade in the process.

Once you gone advanced, someone might just create a special animation for these grenades, turning them into real bola grenades. Just like the "Rocket launchers" mod.

3. Everyone has a pistol, with ammo and skill related to them. For this, I really recommended to just make all classes can equip pistol as their secondary while at same time deleting pistol from default inventory. If asked why, this is due to secondary slot often already used for the classes sub-weapons. So now pistol only presents as an "utility" item.

You should make a "custom" tiered pistols (special type, eg: XCGTPistol) which do not have the normal "PistolStandardShot" but instead an "ability" that fires a standard shot with charges. How to do this? Well the sawn off shotgun from LW2 can do the work. But it is not effective since it is NOT reloadable. What I can suggest instead is a pistol that takes "focus" when you shoot or use related ability and has another ability that fully recharges the "focus". Where to find this? WarlockFocus and WarlockLevel are the answer, Just need to make the WarlockFocus to be able repeatedly activated, costs 1 AP. Where the shoot from? Templar Ghost's Rend may become example. Where to attach the abilities? Well some can take spaces on the soldier, others can be attached to the pistol.

That's it, you got the "ammo" indicator for your pistol too now. For this I already tested with the Utility Slot Sidearms Extended mod. That mod will generate a utility-slot pistol for every tier pistol research you made (not based on pistol you added to inventory by AddItem console or enemy drops like the AlienHunter pistol). Then attach the focus and removing the standard shot
Now, just to make the custom ability to regain the focus and for the "standard shot" replica....

But if you really intended to assert multiple weapons, the "Doom Slayer" mod has it:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2064234140
You should check the weapon swap and "rage" mechanism which actually focus bar.

4. Custom field weapon can be done by borrowing the "grenade airdrop" from LW2. Set it to grant certain "special heavy weapon" instead which resembles both the torque bow and boomshot launcher. Make sure everyone got empty heavy weapon too.

5. Cone overwatch; Now this is the hard part. It has several features along.

• It can attack as many times as much your AP left => Skirmisher Waylay. But the original cone-overwatch in XCom does not follow this rule. So instead, I actually recommended to take example of Area Suppression from LW2. This is a "shaped" overwatch, with target limit too. Now, you just need to shape the zone into a cone and set the target limit to follow Waylay behaviour.
  
• Different weapon means different range and radius => Gotta make copies of this..., gonna have "Sniper overwatch", "Rifle overwatch", "Shotgun overwatch", etc.
  
• Pistol overwatch can be ignored. Remember, you have numbers of 6 here instead just 4 squad.

6. Abilities from gears; Some important abilities comes from gears equipped, such as reload on kill, heal on kill, extra AP on shoot, 100% crit on 1st shot of the turn, etc. You can use the armor/vest slot, utility slots and PCS slot respectively for these effects. Don't forget to make each part unique just like ammo.

7. Lastly, do not hesitate to use 4 or more abilities row / deck and enhance the rank to 8 ranks. RPGO already more than 7, so why you not? If you wary of people needs the random deck, throw it away then. GT doesn't have random ability deck in first place.

Just force the requirement to use the hero promotion screen:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2550561145

For the skill tree, your promotion screen is like this
So you need at least 8 rows there and the standard 7 ranks.
Ref: https://www.gearstactics.com/skills/?class=support

Lets say the first skill pathing "1 to 6" is the right part of GT's Support path (Paragon & Strategist).
Assume that
1A = Empower Lv. 1
2A = Revved Up => Req 1A
2B = Weakpoint => Req 1A
2C = Chainsaw Attack Mastery => Req 1A
3A = Teamwork Lv. 1 => Req 1A, then either 2A OR 2B
3B = Chainsaw Rush => Req 2B
3C = High-Powered Shot Lv. 1 => Req 1A, then either 2B OR 2C
4A = Empower Lv. 2 => Req 3A
4B = Distracting Fire => Req 3C

5A = Teamwork Lv 2 => Req 4A
5B = GT Run and Gun => Req 4A
6A = Chainsaw Command => Req 5A
6B = Lock and Load => Req 4A


5C = High-Powered Shot Lv. 2 => Req 4B
5D = Hone in => Req 4B
6C = High-Powered Shot Lv. 3 => Req 5C
6D = Surge => Req 4B

Up to here should be enough. Now then, The problem is the bolded part.

Since afaik, Xcom2 natively does not have a method to create an "either - OR" part branching like GT skill tree, this might gets a bit difficult too. First, you have to make item that actually granted the specific ability of the specific class from the very start. Due to this, each character may need likea few extra "hidden" utility slots. Take example of "Tank mod" for this.

You need to create something like Icarus Armor's jump ability which has charges on the ability, separated by cooldown at same time and a free action. You will need like 20 unique "Icarus Armor" each with abilities due to 4 abilities x 5 classes. Can be separated by each class main weapon for easier usage, reducing to 4.

These "utility" automatically eats 4 charges to grant the REAL ability (passive/active) at the start of the battle (kinda like Rend's Arc Wave to Focus stack activation). Now, each of these Icarus Armor starts with only 1 charge of the ability, so it never have enough charge to activate this.

But, activating the skill before it grants this armor a charge and then the respective "Fake" ability in promotion grants another 2 so you can have 4 charges enough (and 5 if you have activated both predecessor abilities). But taking both predecessor ability does not grant enough charge (3, still lost 1)
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eg: by taking for example either Weakpoint or Revved Up, each actually adding a 1 charge to the item granting the real "Teamwork Lv. 1" ability. Activating the fake "Teamwork Lv. 1" in promotion screen itself grants 2 charges to the item. => total 4, the teamwork Lv. 1 now can be granted by

Then about the "Prerequisite" lock on the promo screen, the answer is none. All those with "OR" prerequisite can not be hard locked. So High Powered Shot Lv.1 can only be locked by 1A, that is all.

You can't do anything about it. All you can do is write a text in the fake ability screen so people don't take skills in wrong way (eg: promoting 3C despite taking 2A before => fail, 3C can not activate) and sort the promotion screen properly.
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On the other side, you can also ignore entirely and let people have a bit " buff " of free picking the skill they wanted for lower level up to Sergeant rank. The T4 (5th rank) requirement will ensure people not jumping tracks at the higher rank 5 and 6 (7th rank Colonel). Then if there is failure, the AWC system will handle it.

Since the Squaddie slot has 7 empty squares, you can insert the permanent overdrive, pistol skills, custom overwatch, etc into there.

Anyway, with all skills there, it is easier to adjust the mod content. Adding or expanding is easier than compressing/removing after all. Might as well turn XCom to have that 3 - 5 digits HP.