I was extremely skeptical when I read Treebeard at first. He's so high of a threat, I wasn't sure I'd ever really have a good place for him. But I wanted to make a mono-Lore deck, as its been my favorite sphere so far, and I wanted someone that could take a hit, attack, or quest. Originally the 3rd character was Glorfindel instead of Denethor, thinking Treebeard's 3 def + ent allies liking to defend would be good enough. I quickly found out that using Treebeard to defend is the biggest waste for him.
Basic idea of the deck is to prioritize Magic Ring on Treebeard, hoard Dam Bursts until the most crucial turn, and get healing out before ents (with Wellinghall Preserver being the best ally for the deck). With 27 threat, you dodge some mobs, but I've been running this deck through Lost Realms and Angmar Awakened cycle (with 2 quests left), and there's enough threat raising that Pippin almost never triggers.
I could see going a few other directions with Treebeard. I could see running Spirit to get Unexpected Courage. However, I only have 1 core, so that's only a 1-of max for me. I could see going Sam Gamgee instead of one of the other heroes to run a few hobbit attachments and include 3x Cram for Treebeard to have a little more readying, plus the core set "exhaust a hero to ready a hero" card. I could also see going Tactics for more ents, but I think running both Treebeard and Quickbeam would be such a high threat that you wouldn't have the time. The only game I've lost with the deck was due to hitting 50 threat a turn before I'd win, and I've never ended a quest with less than 43 threat.
This deck is my second truly successful deck (I've taken Hobbits through all of Harad and about half of Saga with only a few second or third tries). As I've said, I could see playing around with expanding out from Lore, but losing the ability to play Wellinghall Preserver, Self Preservation, or Daughter of Nimrodel on turn 1 would be rough. Overall, this deck has been a lot of fun so far.