The only reason that chess is balanced today is that the teams have the same pieces. Any game would be balanced if the board is symmetric and both sides pieces are the same. The issue is who goes first.
You can't just add 5 new races to the game and expect it to work out perfectly.
Agreed, however it may make it more interesting to a lot of people.
If balance is only about equal chances, then chess actually rates poorly - White wins about 1/3 more often than Black. War (the card game) or rock-paper-scissors can both boast a considerably better balance :)
So if we talk about balance in chess, I think we mean something deeper than your view of the concept: the harmony between its different aspects, like attack vs defence, strategical vs tactical thinking, calculation vs aesthetics etc.
More like balance in art.
A "well-balanced painting" is not simply the most symmetrical one :) That's the easiest thing to achieve, but that's not the point, I believe
You can't just add 5 new races to the game and expect it to work out perfectly.
Agreed, however it may make it more interesting to a lot of people.