I'm going to ask a question, and please don't think this is snarky or meant sarcastically; I really do want to pose it as a genuine question and thought exercise, especially since I don't know what the right answer is, or even if there is a right answer.
Let's say you're in a party to do a savage fight, and you're struggling a bit with the mechanics. You keep messing up one specific thing, and -- this being savage -- one person messing up can often mean the entire party wipes (because now someone takes two tethers/AoEs/strikes/Protean beams/whatever). You're convinced you can learn the mechanic with a few more tries, probably. It's been an hour, though, and the party's gotten frustrated with the inability to progress further.
Would you prefer that they just silently leave the instance and kick you from the party to find a new person? Or would you prefer that they offer advice on how to get through the mechanic?
(Again: I don't mean this facetiously. I know some people genuinely might prefer being silently dismissed and left to find a new party, rather than feeling like they were called up in front of the class, metaphorically, and critiqued.)
Now envision scenario two. You know the mechanics, yay! The party keeps making it to enrage! But they're making it to enrage with the boss still at like... 11% health. If that's happening without a whole bunch of deaths to mechanics, then it means somewhere, the party is missing the DPS needed to clear the fight. So unless something changes, it's mathematically impossible for the group to clear this fight. Would it be better to just keep pulling endlessly, hoping that somehow, more DPS appears? Even if you know it's pretty much doomed?
Now let's say you can tell it's the black mage. You don't even need a DPS meter necessarily; you can just see that the black mage is not using their mobility tools; when they need to move for mechanics, they simply stop casting, run around until they reach their spot, and only then start casting again. Would it be better to pull the black mage aside and offer advice? Or would it be better to just silently kick them from the party and replace them?
And I ask this genuinely, because I have also been the person who puts together a PF for a clear party before, and so who is the party lead and responsible for these sort of choices. Like, I'm honestly curious... if it becomes obvious the party will not achieve those goals for whatever reason -- failure to do mechanics, one person dying repeatedly, whatever; it doesn't have to be DPS-related -- is it better to ask if someone needs advice/help, even if that's unsolicited?
Or is it better to 'not butt in' and simply kick them from the party silently and with no explanation -- but also without potentially publicly embarrassing them by 'sticking your nose in their business' and asking what they're having trouble with -- in order to find a more viable party member?
I know that even though I consider myself a patient person, if it becomes manifestly obvious a group is not going to progress further in the fight but people keep just blindly beating their head against a wall for an hour and a half despite that... I admit, I can start to become a little grumpy around the hour-and-fifteen-minute mark or so, simply because I don't have infinite free time, and if I'm throwing that time at savage I want ideally to make at least some progress during that time. So I definitely do understand why, if it's obvious that a specific person in the party is functionally guaranteeing no further progress will happen unless something changes, people are going to want to do something to address that situation.
As noted elsewhere in this thread, I don't think an ACT-style DPS meter is the right solution (or even really a viable one) for a variety of reasons. But I also don't think "silently keep slamming your head into a brick wall even knowing the wall isn't going to crumble before your head does" -- i.e., keep doing pull after pull even when it becomes clear one out of the eight folks in a party is going to prevent further progress entirely unless they change something about what they're doing -- is necessarily the right answer either.