How do we know this is an exploit? The tree and branch is there for a reason maybe this is just using environment as a strategy. It doesn't effect boss in any way he actually can still hit healer with magic.

That's like saying on the final boss, hiding behind pillars is an exploit because it prevents you from getting hit from catastrophe. Again, using environment to your advantage. Bosses not attacking, getting stuck, etc is totally different. But groups should not force or pressure anyone to do anything. I always ask if healer wants to jump up there, if they say no, it's not a problem and we just deal with adds.

The problem isn't the "exploit", it's the people pressuring those to do things a certain way that doesn't have to be done in that certain way.