It is not about being realistic or not. That's not the point. The point is the AI could have ground his artillery units into mincemeat if it kept on fighting. Buzzdowan had no air defense whatsoever, and would not have any for like 30 turns. The whole thing is about the AI giving in with a huge tech advantage. And not only that, giving up its capital freely. The whole thing is absurd.
It's almost as bad as the Red Sox trading away their star players.
Total War is also completely different, but if your comparing AIs. Mods are needed to make the AI better in that game. Lately, with the new versions of Darth Mod, ETW, NTW, and especially Shogun 2, have made huge strides in the AI department. Blowing CiV AI out of the water completely. It is not even comparable. The Total War AI comes after you and does not give in. The CiV AI wears a very short skirt lately.