Here's the numbers.
2x is an overstatement for immortal. On Deity, yes, they get close to half your penalties and double your bonuses.
Of particular significance on Deity:
- AI starts with 2 settlers, 2 workers, 2 military units
- AI has a 50% modifier to buildings and national wonders (can build buildings for half your cost but NOT wonders)
- AI gets 60% combat bonus vs. Barbarians
- AI gets 5 free techs, basically everything they need to build roads, mines, pastures, shrines, granaries, immediately. Gives them a huge edge with 2 starting workers
- AI gets 60% modifier to unhappiness (so 40% less then you)
- AI only needs 60% of the food you need to grow
- AI gets a 50% discount to building units and buying them with faith
- AI gets 50% discount to building and unit maintenance costs
These are the ones I understand, there are other modifiers whose purpose I'm unclear on. Given the list it's amazing they lose at all. Shows how dumb they are at management. If they could tech near as optimally as a human and fight better humans would lose every game to early T40 rush. Given the huge bonus they get starting with workers AND the tech to use them, this is why stealing their workers is so effective at nerfing them. If you manage to steal both you can see the effect as they are the weakest AI by far by turn 100. This is a recommended move for aggressive Deity/Liberty strategies on standard maps.