Many heroes have stuns, and the giant doesn't have much stun resist. If you don't have an Occultist to debuff damage dealt to the giant, this means you're probably going to rely on stuns. Second, you need a way to deal with that giant tree being swung at you.

He really is quite terrible in the Weald. The Leper can't even hit the hag boss or backrow torch bandit with the cannon boss. Man of Arms+Hellion, heroes you could have been using instead, can charge forward. A Leper in here for example is probably not the best choice. Firstly you want heroes that fix their positions without wasting turns. After healing from death's door because of this, you're now crippled for the rest of the run. Even with regular hits, a 20-40 swing can 1 hit quit any hero if they aren't topped off. I've seen it crit 60, which is instant death's door for any hero.

The next problem is that giant tree he likes to swing.

There's 2 problems, firstly, they can shuffle your whole party anytime they feel like it, and unless you have a high move resist across the board, you'll never see it fail to totally screw your row. I personally plow this place without much concern until I run into a tree giant. They may not be as dangerous as the bosses, but since you have to fight them first(and can end up fighting several per run), it's a problem when they cripple your party before even reaching the boss. Everything else in here isn't even a threat by comparison. You need a way to deal with these things, or they can wreck a totally perfect ruin singlehandedly. Only problem I've ever had in the Weald is vs the tree giants.

What to bring to weald darkest dungeon