Riot doesn't need to make every champ balanced on every map/mode. If you can draft pick, the top 6 champs accused of being OP will be removed. It balances itself. With draft, on TT, no one can legit complain about OP because we won't be seeing much of Tryn, Shaco, Singed, Amumu, Mundo, etc. on that map.
Most importantly, I'll hear a lot less of the chronic whiner's paradox: "Boo-hoo, I'm getting schooled because you're a noob."
Come to think of it, 3 bans per team on 3v3 means each player could choose 1 ban, which would be pretty cool.