The current example I'm thinking of is the one with the Minotaur and the "bait" from The Fractal Continuum. One of the other players, eg the healer, would activate this, to interrupt an AOE with heavy damage, where the Minotaur goes after the bait add, and if it successfully eats it, recovers HP.
Re-apply this to a different scenario where the healer is 'gaol'-ed and if the tank goes to free the healer, the boss instead eats the healer if brought close (which is a mechanic like the meteors in T9, combined with the The Lost City of Amdapor when a player is "eaten", and if not freed, immediately ko'd mechanic) and recovers significant HP.
Now either the strategy would be "keep the boss away from the gaol'd healer", by which when the healer sees it coming, moves to the edge of the arena, and the tank keeps the boss on the other side. This buys the most time for the DPS to free the healer. The second "faster" strategy would be to let the healer die before the mechanic comes up, and the mechanic can thus be skipped, but is no fun for the healer, and would require players to self-heal for the entire fight. Hence a properly balanced version of the fight would not allow the second strategy to work even when over geared.
However the other type of fight I was thinking of was one where the healer is simply removed from the fight during phase 2 (eg boss at 60%) and has to do something like "heal a npc (like the magic pot)" to free themselves, that they are otherwise taking AOE damage in a separate room while the weaker DPS is paired with a weaker mini boss in a walled off arena, the stronger DPS is paired with a stronger miniboss in a walled off arena, and the tank keeps the main boss busy (but can do extra damage during this phase by dropping tank stance.) If the DPS fail their mechanics, then they are not available to be raised, as they are not returned to the main arena until the boss's HP is 50%. So the penalty to failing the dps requirement is that the DPS is not available to help speed up the fight. If the healer fails their mechanic (eg if the healable target dies, they're locked in the room until the main boss hits 50%. They can also die by not healing themselves and still not get returned to the main arena until the main boss is 50%.) At 50%, the boss "summons" all the players back into the arena if they're not there, and switches to a "pads!" type of mechanic that requires all 4 players to stand somewhere to toggle a shield, and if players are KO'd from failing their mechanics, then this mechanic fails, and whoever is remaining takes heavy damage going into phase three of the fight, potentially failing it here. If the tank manages to get the boss from 60% to 50% before the DPS kill their mini-bosses, then the mini-bosses are also pulled to the main arena, potentially knocking them off the "pads!" mechanic.
Like what I think needs to happen is that in, say V5.0 they make all the "easy" storyline dungeons 8-player exploratory content, while putting more actual things to do into those dungeons to split the party so they're a bit longer (put role checks in place where only the healer can walk through this door), while some "savage" tier content are 4-player fights with more rigidly defined roles with bosses that you can't eat mechanics on.