I mean no disrespect, but why not simply put together the race you want, with abilities you feel are balanced, and leave others who feel otherwise to build the races in as unbalanced or balanced a fashion as they desire?
You don't think there's inherent value in a balanced game, with balanced factions to the extent that it's possible to do? Right now from a pure gameplay perspective, the Stock races have little appeal outside of Lore, because you can effortlessly make a better one.
Custom Sovereign creation shouldn't be about making a better Race in every case, but a different one. I'd just like to see something put in place to make sure the Stock races always had some value to play over a custom race, and that people didn't automatically assume playing through the game as a custom Sov was a lesser achievement. Because, currently, it is.
Otherwise, from a gameplay perspective, you really might as well get rid of the Stock factions altogether, and just let people make their own, if the Stock races are going to be an inferior option every time.
To an extent, this was the way it was in the Gal Civ 2 games. Stock races sometimes had abilities and bonuses greater than what could be assembled in the custom race maker. The balance was, with a custom race you had complete control over what you put where, which is a big advantage.
Again, I don't mean this as an excuse not to balance the individual abilities amongst themselves, which I also hope happens to the degree it is possible to do.