Let's see what's going on:
https://demos.potato.tf/mvm_derelict_rc2_int_defragmentation_1562876836.dem

I closed out of the game before I copy time tables. Oops.
Well you are a little over 20 minutes with this mission and in my opinion, the time is well spent.

2 hitches however

A wave that starts very easily with almost naught but bison soldiers. They're not exactly painfull or resiliant on their on even in big numbers, infact alot of them died before even reaching the sentry (the sentry they can barely scratch because 20% dmg vs buildings).

Another sees a very slow and anticlimatic ending with 6 Giant FaN scouts and meager FaN support backing it up. To be honest, these guys felt like they were supposed to be aiding prehaps another giant/squad/tank rather than be the main force itself.

Demonstration:
https://demos.potato.tf/mvm_goldpit_b12_adv_goldrush_1561915237.dem
Demonstration of redoing W6, this time without an engie going afk for 4 minutes during:
https://demos.potato.tf/mvm_goldpit_b12_adv_goldrush_1561918144.dem

Total wave time breakdown for: mvm_goldpit_b12_adv_goldrush
[Victory] Time spent on Wave 1: 3 min 27 sec
[Victory] Time spent on Wave 2: 4 min 33 sec
[Victory] Time spent on Wave 3: 6 min 48 sec
[Victory] Time spent on Wave 4: 4 min 45 sec
[Victory] Time spent on Wave 5: 5 min 42 sec
[Victory] Time spent on Wave 6: 5 min 3 sec (panic button)
Total success time in mission: 30 min 18 sec (100%)
Total time spent in mission: 30 min 18 sec

[Victory] Time spent on Wave 6: 5 min 7 sec (redo)
Total success time in mission: 5 min 7 sec (100%)


After running this mission balance-test style I have only 1 complaint
W6:
Lower the pyro boss' hp by atleast 10k. Atm balance testing has us making close calls to the hatch. Should this change go through I'd like to re-run wave 6 just to be certain.
Should this nerf work then it'll be a pass from me

Would you look at that demo!:
https://demos.potato.tf/mvm_brugge_rc1_adv_funeral_toll_1561910721.dem

General:
Frequently this seems to suffer from support/small bot spam, don't underestimate these little guys as their combined health and firepower is still to be considered

mvm_brugge_rc1_adv_funeral_toll
[Victory] Time spent on Wave 1: 4 min 8 sec
[Failure] Time spent on Wave 2: 4 min 22 sec
[Failure] Time spent on Wave 2: 4 min 44 sec
[Victory] Time spent on Wave 2: 4 min 24 sec
[Victory] Time spent on Wave 3: 3 min 21 sec
[Victory] Time spent on Wave 4: 5 min 45 sec
[Victory] Time spent on Wave 5: 5 min 14 sec
[Failure] Time spent on Wave 6: 5 min 4 sec
[Victory] Time spent on Wave 6: 4 min 27 sec
[Victory] Time spent on Wave 7: 1 min 10 sec
Total success time in mission: 28 min 29 sec (66%)
Total time spent in mission: 42 min 39 sec

W2:
What a spike in difficulty, now that the rate of bots isn't being slowed down by them hugging the box it has become an unrelenting assualt of bots. The rate of bots both big and small being thrown at us is painfull
-Considering toning the small bots, less backscatter scout for example
-The semi-giant burstfire shotguns really pack a punch, and with the numbers they're deployed in they are very threathning

W5:
-The last 6 dragon fury pyro's take rather long to chew through as they spawn very slowly one after another

W6:
-That burstfire support is really brutal once the final heavy+medic pairs start rolling out. Consider spawning less of them with longer waits, or use regular demoman, something to neuter their total firepower
-With it's current difficulty the last heavy+medic combo should really be kept to 1 repetition

Map:
At this points i have no complaints regarding the map itself and has my vote for art-passing

General:
-Somany bots forcing themselves through the middle flank makes holding the U turns on either side of the map very difficult. are the bots flanking us on their volition

mvm_aircrap_a5_adv_aerial_stupidity
[Victory] Time spent on Wave 1: 4 min 37 sec
[Failure] Time spent on Wave 2: 2 min 28 sec
[Victory] Time spent on Wave 2: 4 min 3 sec
[Victory] Time spent on Wave 3: 4 min 37 sec
[Victory] Time spent on Wave 4: 3 min
[Victory] Time spent on Wave 5: 8 min 26 sec
Total success time in mission: 24 min 43 sec (90%)
Total time spent in mission: 27 min 11 sec

W1:
-All these soldiers make for quite alot of firepower
-With all this action going on, you could probs skimp on the spies
-Those scouts taking the flank are suprisingly painfull in their current numbers

W2:
-Supposedly, one of the giant heavies almost took the flanking route
-The part following the pyro's is quite brutal and cost us 1 attempt

W3:
-Poop toots taking us up the pooper by flanking us is quite painfull

W5:
-your scout boss sure seemed hessitant to get down

Well W1 doesn't persé need an air-raid of al things, but it could so with atleast some bots coming from a different place. atm everything bottlenecks through their spawn and dies as soon as they leave it, what with few not-that-threathening bots this is an easy hold even with 4 people.
You can get so aggresive you can litteraly spawncamp this wave

Patch up your nav a bit, notabely:
-the mysterious wall things gets stuck on/hump furiously
-having bots actually walk down the ramp, instead of just jumping of it
Implement the staircase we discussed about near the choke that is the factory's enterance to easily allow the non-blast jumping plebians to get on the catwalks faster.

When those are done you have may have it with the artpass.

Don't defenstrate the demonstrate:
https://demos.potato.tf/mvm_meltdown_rc4_int_collapsing_cores_1560540811.dem

mvm_meltdown_rc4_int_collapsing_cores
[Victory] Time spent on Wave 1: 3 min
[Victory] Time spent on Wave 2: 2 min 29 sec
[Victory] Time spent on Wave 3: 2 min 25 sec
[Victory] Time spent on Wave 4: 3 min 17 sec
[Victory] Time spent on Wave 5: 2 min 40 sec
[Victory] Time spent on Wave 6: 3 min 10 sec
Total success time in mission: 17 min 1 sec (100%)
Total time spent in mission: 17 min 1 sec

While we did trash test it, it was with 6 people having at it who weren't trash testing all that hard a pinch of salt is to be taken.
While we usually suggest watching the demo, right now I especially suggest you do to bring your own 2 cents into the matter

At 17 minutes it's really on the shorter side of things, might be written of "6 players not trashing hard enough" but you might wanna look into oppurtinities to buy some time.

We didn't encounter many problems and it's up for a balance test in the hopes to either reveal underlying issues or to destory my fears.

Last wave might have a rather beefy tank and boss to boot, even when nigh the entire team were on it, it seemed to make quite some progress despite the lack of anything backing it up.
Same goes for the boss. This is with 6 people wailling away at it, the balance test 4 people setup might find itself struggling

Reviewed the demo so that I can leave my vote,

sntr forgot to mention:

W2:
100% resistance vaccinators. We prefer your use 80%, 90%, something not-100% as to not turn into a game of "where is the class that can damage this dude at?" or have players resort to suicidal tactics to get at them

Mapwise, it recieved the last vote it needed for artpassing so you go ham with making this thing pretty

also W3:
Why were the scorchshots sooo sloooow. I am not sure if they were supposed to be aiding the flareguns but with the scorch's speed they just end up eating the flare's dust, get left alone and become easy pickings.

I have to ask, is general unbreakable intended to take this much self-damage? The difficulty is still propper even with him killing himself, I am just curious if this was your intention as it makes killing him just that much easier