Honestly I find it hard to believe many of you won't be right about awful balance and AI. I remember previous releases too clearly. Civ 5's near release demonstration of the 1upt combat on the map of the Nile region, with the AI very foolishly feeding its troops into a bottleneck meatgrinder. Many were dismayed, others hopeful for improvement before release. Nothing changed before release of course. This doesn't trouble me though.
I think it may be slightly better this time since they seem to have built off Civ5 a little more closely, and have hopefully been able to carry over much of the benefits of so many years of optimization. But it's still unlikely going to be much better than we see.
That being said, I don't think it's worth worrying about. It will be optimized in time, Firaxis, with only one moderate exception has a great track record of refinement. If you want to like the game, just keep that in mind. There's no need for wild expectations here, the process is all pretty set in stone. Our expectations aught to be pretty tempered by now.
great games take time, and you can't develop in a vacuum forever.