I get the feeling that the AI already knows how to tech well. In each of my games there's always been one or two AI civs that start charging away in tech. However, I'd also agree that there's definitely a case where some of the AI civs seem to stagnate a little. This could be from a couple of reasons, namely:
1. They could be spending too much in performing rather ineffectual espionage missions. I've still yet to have the AI steal a tech from me, but if it were able to save and focus its EPs a little better and steal a tech or two, then that would make its tendency to indulge in espionage more worthwhile. If the AI is just arbitrarily spending EP points on poisoning my water or destroying my farm, then it's just wasting commerce in my opinion. These are ok options only once in a while. There should be method behind the madness, and I'm not convinced there is, yet. If espionage was a bit more effective, say, then maybe even the human would better value allocating the commerce to, at the very, protect themselves from AI espionage.
2. No tech brokering. This certainly leads to increasing tech disparity as the game progresses. When techs are relatively cheap and abundant, and it's before Alphabet, disparity between civs isn't that great. However, as the game progresses to the later stages, the tech leaders begin to have a huge advantage with this option on. They can effectively monopolise how the slower teching civs progress, knowing full well that tech traded to them in this manner can never be used by the beneficiary. I like the no tech brokering option, but I definitely feel it gives a distinct advantage to the 'faster' teching civs, in which the human will more than likely be one.
Does anyone have some more concrete evidence of this, i.e. having played BtS with No tech brokering on and off under the same settings (map type, speed, difficulty level)?
Cheers