That still sounds like a timer to me. The difference between a dungeon and a raid is that the entire dungeon is “one encounter” as opposed to one boss fight. The dungeon has an enrage timer after which point you fail.
The only difference I can see is that you get more rewards by being faster rather than being a binary pass/fail metric. Even in this case though, assuming you want to get the maximum rewards, the goal of the dungeon is not in fact to beat it as fast as possible, it’s to beat the +3 timer. Compare that to the MDI where the goal IS to complete it as fast as possible. There’s a subtle difference there. Instead of time being the objective, it becomes a resource. Which means there are times when you can spend that time on safety so long as you don’t go over budget.
The part that I think the community does not understand is this means there are some strategies that are optimal in MDI that are not optimal in your average M+ PuG run. Despite what GD would have you believe, M+ is not a speed run just because it has a timer. Beating the +3 time by 2 seconds is just as good as beating it by 2 minutes. You shouldn’t always choose speed over safety if you have time to spare - especially if you don’t know the specifics of what the MDI teams are doing which make their strategies safer or more consistent than they might initially appear. No one takes stupid risks in MDI, if they’re doing something it’s because they have a fairly decent expectation that it’ll work.
But the thing is that even if your goal is safety and not speed, damage is still valuable. Shorter fights are safer than longer ones. The shorter a fight is the fewer opportunities there are for someone to slip up and make a fatal mistake or for a bad mechanics overlap to happen. By contrast, tanking and healer have diminishing returns. You only want as much tanking and healing capability to the point where you stop dying. Anything more is superfluous. That’s why DPS is the most numerous role in any group and why it’s the first role people look to add once their other bases are covered. So even in this world where our goal isn’t to speed run, healers should still do damage when it is safe to do so.