I would like to preface this post by saying that I have no problem with how the current raid bosses are done, but I would like to offer an idea which would enable most builds to have a reasonable chance at a boss but not trivialize the encounter.
My idea is not a boss that would require all builds, e.g. Vale Guardian split, where a group requires a mix of direct damage, condi damage and CC, but one that can be tackled with a just one build type but having the mechanics work against them.
The boss has 3 (or 4) states:
Damaged by direct damage
Damaged by condi damage
Damaged by breaking breakbar (a variation could be a temporary BB which is quick to break and causes small/moderate damage, and a long-lasting BB which is very hard to break but causes massive damage when broken)
The mechanic is that the boss would constantly swap between states, and the team would have to perform some task/action (while under fire) to switch him to the stage that they are built to damage. The tuning would be to make it do-able if your whole team was built around one of the stages but impossible if you can’t get it into that particular stage. I envisage this would let almost any build type to succeed but still require the players to be good and dedicated.
Comments/ideas/improvements welcome