You have read a single example Shurrikhan made, while ignoring the examples made by me in the original post.
There are many ways to deal with these issues. Have the boss do major cleaves, so no, the tank or healer couldn't deal with the adds, cause tank trying to do that would get the DPS killed. Healer trying to do that would get the tank killed. Another part is separating the tank and healer with DPS. There are already parts where groups are separated, mainly in raids. What is the problem of making an encounter here or there where DPS have to do actual mechanics, and end up being separated as a result? For example, a floodgate would be open with Sahagin boss. Either close the floodgates or boss goes into enrage once the water rises, being in his environment. Whoever goes however ends up trapped and have to deal with the adds. They die, the adds will be "free" and go after the healer. They kill the adds, good for them, no need to die and extend the battle.
Then there is a battle where widely-understood mitigation matters. At that point, DPS's role would be largely avoiding the AoE's (a form of mitigation) and probably triggering mechanics, like turning off turrets, which would give X points towards the win.
Another example is a battle where mitigation matters instead of survival, with adds, hence the team would need to balance between killing adds and keeping them alive. Kill too many and the battle will take ages. Kill too few and you will be overwhelmed. Tank exits tank stance or uses cooldowns poorly (like using them with few adds to deal with a single tank-buster instead of waiting for a long-term, sustained damage with more adds), the battle will go slower. Healer will have to focus on healing, because the more adds there are, the more damage, the higher mitigation accumulates, the sooner the battle ends. And DPS'ing when the party decides the magnitude of incoming damage is just nonsensical. And DPS?! They kill the adds to control their amount and try not to get killed themselves.
In case you didn't notice, this thread is about ideas that COULD be in the game, not about what is in it.
And what I am talking about is using those "not be killed" stats to determine the winner, instead of those "to kill". There is nothing wrong with it. Nothing unusual, lore-wise or technically. It would just switch the focus from one stat that already exists to another stat that already exists. NO CHANGE is needed for the system at all, just adding a counter for damage mitigated/avoided/dodged and a flag that calls the players the victors once a certain threshold is reached. As for battles based on time, there are already quests where you go against unending waves of enemies and need to survive for a certain time. The only change necessary would be adding a penalty (adding time to the counter) on someone's death. Trifling matter.
This is just ridiculous. The goal is to deplete their HP bar...but that's the very reason why I suggested changing that goal...Again, this is not about what IS in the game, it's about what COULD be in game.
And being at war means NOTHING. Most soldiers on the battlefield surrender once they know they have no chance of winning. That's the very essence of what I'm talking about. I'm not talking about changing a wild beast on a rampage to suddenly up and stop. I'm talking about SOME bosses, usually intelligent, but also use arguments that something else comes and scares the boss away after a while, like a bigger beast that have little interest in the party.
You having little will to think about options, or poor imagination, doesn't mean there is no way to make DPS have a purpose, as examples above show.
The story is not made like that, and suggestions and ideas are usually for things that are not present in gameplay, so it's obvious it is different than what we currently have. And there is no need for any core modification. It's nearly entirely a design-based "problem". Making Palace of the Dead or a new PvP mode requires far more effort and change than what I brought up.