In terms of boss balancing for HM +6 gear with my current knowledge having taken down boss 1 + 2, and have seen boss 3, 4;
Boss 1 is in a good place. not easy but with a good coordinated group and some practice we can do it.
Boss 3 without the experience of doing a full fight, it seems like it will be good. The difficulty comes in managing everything. Working out how to position so that sky suns can be hit/ got to, grouping for when the sun comes down, killing the boss, killing the consume adds in time whilst also killing suns.
Boss 4 having only tried to fight it once so far seems hard. It should be hard and it is. The main difficulty comes from the adds constantly spawning and being able to heal. At first impression it’s possibly too hard but I want to try again with a full experienced group before asking for change. I haven’t seen what hell is like but seeing as the last hell on normal mode wipes groups I can’t wait to see whats in store.
Boss 2 is too easy for +6. From my DPS perspective, the difficult comes in dodging jumps, pools, avoiding chains, kiting the boss charge, keeping healed from chain tick dmg and hitting the boss when its moving/charging. The fight starts easy but progressively gets harder, But it then resets most of that difficulty when the pools despawn.
I would like to see the pools changed to be permanent throughout the fight. My reasoning behind this would be; It would act like a soft limit to how long the fight can go, we would have to think more strategically about where to drop pools and would make it slowly harder and harder to kite and manage chains.