I know this is probably impossible to implement now but I think world bosses, aside from being hard, should be more of an even and less of a punching bag. Let’s take the Shatterer for example.
You do several quests and as a reward he comes out for a punching match. He sits there.
Now imagine if he pushed in and you couldn’t even damage him right away. If it was all about pushing him and his forced back into a position. You could even have two separate objectives going at the same time so that you could watch groups have to think about which one needed help more. Finally working toward actually fighting him.
And the fight should have serious consequences. Failure should be possible and set the area back a lot.
I have yet to see anyone fail a world boss. They should be the toughest but they are pretty much the easiest.