EndTimes, I don't play tablet games to be burdened by the ownership of my choices. ;-) And I think a lot of people coming out of Bronze Age don't know enough to make an optimal choice, nor do the brief nationality descriptions complete their understanding. It would be one thing if this was a game like Civ that you might start afresh over and over. But this is a one time choice for a game that they hope you will continue to play for a year or more.
Skillz, if allowing people to change nations "ruins the game mechanics" then that probably means there are optimal nations at certain stages, like the Greeks and Romans. So then people who don't choose those end up relatively punished...where's the fun in that? If you ask me, having to live with a poor nation choice while everybody tells you you should have been Greek or Roman is what would ruin the game. And some folks, as they grow disappointed with their choice, will just quit and go back to Clash, etc, which isn't good for any fan of this game, especially the devs.
It seems the devs intend nationalities to cater to play styles, which is great. And like all these games, it might need iterations of further balancing to keep all choices viable. But limiting our ability to explore all the options (regardless of how more "realistic" that makes the game) limits, rather than enhances, our play experience.
Also, I chose Japanese, and now I'm bummed about it. I thought the peace treaties were normally shorter than they are. All you Greeks and Romans can commence smugness now. ;-)