Why is Twisted Treeline so terribly balanced?

same reason dominion was never balanced, just another game mode to have for the sake of having variety. Main focus 5v5.

Because riot only cares about the rift; just look at what happened to dominion in the year before they deleted it.

Cuz it is too small and it makes some champs that hate wide spaces op, and some champs that rely on space weak

Nobody really cares for that mode anyway. Also balancing all champions for several different gamemodes is pretty much impossible so they stick to balance the most popular gamemode.

sarcasm?