Fun fact: every AI game that has had a massive runaway in it (conqueror or not) on the past few patches has been running imperialism. It's too strong right now.
I have to agree with G on this one, although I've seen this more so with militaristic civs that have large amounts of puppets. In a few of the recent games I've played, it's the aggressive conqueror with imperialism policies that is leading in science over rationalism civs. I feel it has to do with the scaling benefits of puppets vs. penalties. A small change to science benefits would be welcomed by me.