The Force in balance doesn't refer to equal parts light and dark. Imagine standing in a canoe. Balance comes from harmony, peace, and serenity. If there is some troll-faced Sith Lord in the boat rocking and generally making a chaotic nuisance of himself, your balance will be disturbed. The Jedi interpreted "balance to the Force" to be something along these lines.
But as I always must bring up in conversations about this topic...
This is a prophecy that misread, could have been!