The other thing about Ents generally is that because they enter play exhausted, they are by default vulnerable to any treacheries or enemies that trigger off exhausted characters.
I can't comment until I play with them, but I think the entering play exhausted is a big downside. A quick deck can beat a lot of quests in 6-7 turns, so Treebeard is coming in for, at most, 5-6 turns. Could two allies first turn that come in ready to rock be more effective in that situation? Quite possibly. Like Leptokurt says, it's a nice new addition to strategy that really opens things up. Ents kick like a mule, but that early game can be so hard they may not come along in time!
