All stats except science, culture and food scale with player era.
I wanted the AIs to be able to snowball with their player era scalings, but since science and culture dictate player era progression I scaled them with game era (except for the extra difficulties) to prevent an overly strong snowball effect.

Differences of this mod to other "smooth difficulty" mods:
AI keeps bonus starting settlers (option to remove them with compensation is there though)
Usage of both game era scaling and player era scaling
Percentage differences rising from early eras to later eras (for example science scaling is 2-16% -> +2% science at Classical era, +4% at Medieval... makes 2+4+6+8+10+12+14+16+=72% percent at Future game era per difficulty above warlord, so 72% at prince at Future game era and 144% at king at Future game era)
Integration of the Real Strategy mod with changes to make it work optimally with it

Deleted the difficulties lower than Prince to make it obvious that they are not affected by this mod
Two extra difficulties added: Pro and Insane

AI Changes:

Early game changes:
Added scouts to starting units on high difficulties
Flat science and culture bonus removed (was 8% per difficulty)
Flat production and gold bonus lowered: from 20% per difficulty to 10%
Flat faith bonus increased: from 8% per difficulty to 10%

Scaling modifiers:
Scaling science bonus added: 3-24% per difficulty and game era
Scaling culture bonus added: 2-16% per difficulty and game era
Scaling production and faith bonus added: 1% per difficulty and researched civic
Scaling amenities in all cities per player era: +1 at every second era at Prince, Emperor, Deity and Insane, starting at Renaisssance
Free eurekas and inspirations per era: 1 at King, Immortal and Pro
Scaling food bonus added: flat +1 per second difficulty and game era, starting at Medieval
Scaling tourism bonus added: 12-84% per difficulty above Prince and game era, starting at medieval era (additional tourism bonus on Deity and above)

City States:
Added difficulty combat bonus to city states (except when using barbarian clans mode because of a bug)
Removed starting walls (but not when using the option to add bonus starting warriors)
Removed city state bonus starting units per difficulty (they don't really need them since the AI is a lot weaker early, most of them will survive the game)

Combat:
Added 3 flat anti-Barbarian combat strength bonus per difficulty
Added 1.5+0.5 gold unit maintenance discount per difficulty above Prince (helps militaristic civs to not go bankrupt/fall behind)
Added unit upgrade discount: 10% less gold per difficulty
Removed unit experience bonuses (makes AI promotion timing consistent over different difficulties, which I like)
Added AI loyalty bonus for cities the AI has not founded: 1 loyalty per difficulty (the AI often loses conquered cities to loyalty otherwise)
The AI gains +1 diplomatic visibility against all civilizations at Nationalism (min. Deity) and at Cold War (min Emperor) to simulate the usage of Spies with listening posts
Added military unit production modifier to different game speeds to balance out combat difficulty (-20% production on online speed, +40% on marathon)

Religious buffs:
1 extra spread on religious units per difficulty above King

Various other modifiers:
Reduced AI district project production by 30% (AI spams projects a lot and it feels bad to get no great people)
+1 Influence point when AI reaches renaissance era and +2 Influence points when AI reaches atomic era per difficulty above Prince (to compensate for the AI usually not updating their government and the player being better at using city states)
Bonus economic policy slot at Political Philosophy
Bonus wildcard policy slot at Ideology
+2 builder movement (to balance out the AI moving their builders back and forth all the time)

The AI gets some important military technologies for free when it is two eras ahead of the technology (meant primarily as a buff for culture civs who often just get overrun when attacked because they are missing key techs). These techs are: Archery, Sailing, Bronze Working, Masonry, Celestial Navigation (not military but sometimes AI skips it), Military Tactics, Printing, Cartography, Ballistics, Steam Power, Flight, Steel, Chemistry, Advanced Flight, Advanced Ballistics, Combined Arms)

Insane AI gets additional +1 production in all cities from the start of the game and +2 food in all cities at classical game era.

Flat growth bonus until medieval era added when bonus settlers are disabled: 10% per difficulty
Flat science and culture bonus until medieval era added when bonus settlers are disabled: 5% per difficulty

A lot of adjustments to Real Strategy to make it work a lot better with this mod.
Several BBG specific changes (not to BBG, just the AI) to make it work a lot better with this mod.

Optional:
AI gets +2 strategic resources per turn upon researching the tech for it
AI gets an additional +4 strategic resources per turn upon reaching a reasonable era (as prevention for the AI paying for resources that are obsolete or them skipping the tech).
"Logical Religion Frequency" option which makes it so only AI with bonuses for religion or AI aiming for a culture/religious victory will build holy sites (enabled by default, works only when also using Real Strategy). Leaders defined as religious are: Chandragupta, Gandhi, Hojo, Peter, Philip, both Saladins, Tamar, Basil, Menelik, Theodora, Gitarja, Jayavarman, Jadwiga).

Buffs to science victory specifically:
Flat space race production bonus added: 15% per difficulty
AI gets some science victory techs for free when they've skipped them so the AI gets all the needed techs more consistently
AI now always does the projects to speed up exoplanet

Secret Societies:
Chorus effect reduced from 20% to 5% for the AI (unnerfed Chorus gives ridiculous yields for the AI because it double dips in modifiers)

Monopolies&Corporations:
Reduced tourism bonuses and removed player tourism bonus (that this mod gives; the monopoly tourism bonuses are unchanged).

Babylon:
Removed AI Babylons ability that nerfs their science and buffs their eurekas. (AI Babylon would have some crazy interactions with the free boosts I give the AI otherwise)

Player changes:
Removed barbarian camp gold scaling (now always 50, I just like the consistency)
Increased passive tourism by 45% after start of Industrial Era to make culture victories a bit easier against the high culture AI