A good start would be to actually make bosses the kind of thing you can’t just cheese. I agree that their attacks could be better, but reducing bosskillers and giving monsters a period of resistance to being further staggered could go a long way on its own to making them feel worthwhile. As in you actually have to engage in the fight like you do with Halescourge(although you’d have to make sure they’re actually fun to fight, too, and I imagine most people don’t like Rasknitt).
Ideally, all of the monster fights and not just lords would be more engaging. You could add checks during fights to ensure the fight isn’t as easy as following a set pattern, they could block and dodge more, they could sweep and intentionally avoid getting surrounded like players would, etc.
Obviously this would be a little overkill with all the adds and hordes that go into these encounters but you could tweak those for sure.