How good, or bad, is Extreme AI on treaty?

I've been playing 20 minute treaties on Extreme AI. I usually win, but it's still competitive up until around 45 minutes in when I have more resources coming in that them (or at least more army coming out).

I tried a 30 minute treaty on Extreme again today, and it was way too easy. At one point I had about 60k in score while they had 19k.

I've noticed, though, that sometimes the AI's score can be very different at any particular point of the game. I don't know if it's dependant on the civ they are or what, but the game I just had felt like I was playing against Moderate on Treaty.

What's up with this? Is the AI bad at 30 minutes plus? Is it dependant on the civ they play as?

What's going on.