Since you asked me for the Facts, let's make a comparison on the bonuses of the AI of Civ 6 Deity and that of Civ 1 Deity (I ignore the various elements that do not influence the AI such as the player's research penalty)
The difficulty level is a game setting in Sid Meier's Civilization that allows players to compete against AI opponents matched to their skills and desire for challenge. In order from lowest to highest, the difficulty levels are as follows: Chieftain ("Chieftan" on the Hall of Fame screen)...
civilization.fandom.com
The difficulty level is a game setting in Civilization VI that allows players to compete against AI opponents matched to their skills and desire for challenge. In order from lowest to highest, the difficulty levels are as follows: Settler Chieftain Warlord Prince (default) King Emperor Immortal...
civilization.fandom.com
Civ 6 Deity
AI
Science/
Culture/
Faith Bonuses = 40%
AI
Production/
Gold Bonuses = 100%
AI Combat Bonus = +4
AI Combat XP = 50%
AI Free Tech/Civics Boosts = 5
AI Starting Settlers = 3 (this is a GREAT BONUS)
AI Starting Builders = 2
Civ 1 Emperor
CP Rows of Food = 8 (The number of rows in the computer player's
food storage box (i.e. how long it will take for a city to grow). The number of rows in the human player's box is always 10)
CP Resource Cost Multiplier = 0.8 (All computer players have their costs to build
units and
city improvements multiplied by this amount.
)
CP Lightbulb Increment Per Advance = +10 (Each time an
advance is discovered, the cost (in lightbulbs) of acquiring the next increases by this amount.)
Look at the AI of Civ 1 (which is certainly not good, I'm not saying this) it doesn't start with 3 Settlers, it doesn't have a +4 combat bonus, it doesn't start with 5 free techs, it doesn't start with 5 additional units (this is is another notable bonus given that in Civ 1 it is a Stack and Civ 6 has the 1UPT) yet the AI of Civ (which I remember WAS RELEASED IN 1990) is capable of conquering cities, while the AI of CIV 6 NO
How do you explain it?