I'm firmly on the side of 'just communicate' which, to me seems relatively easy, but i also understand that might be troublesome for others. I've been the insecure tank at later dungeons purely out of anxiety, I've also been the insecure and later confident healer, and a generally confident DPS, so I've tried out most roles. As a DPS, I've never had an issue with a tank playing more timid. As a healer, I've never really had a problem with a tank being a little slow, or a little bit silly, or a little bit uncaring in regards to their gear or mits or whatever. Idunno, I think if I spot a tank being unsure, I've told them when I was a healer they are free to pull more if they feel comfortable, but I've also had zero issue with them politely declining, or even not saying anything in chat.
I have anxiety, but I love MMOs very much. I know I'm not the only one who is like this, and I understand some of the critique given by other players who feel as though they don't owe anyone their time if they think the dungeons are going too slow. I think in a way, everyone has a point, to some extent? I dont' think anyone's necessarily wrong for feeling this way, I've definitely encountered some people who didn't know what job stones were in like. Stormblood content. It just happens. I'm not in a rush, but others might be, but again, I think the point is to try and meet people where they're at, if you can. I think if people leave it's their prerogative, but I also disagree with the idea that others are playing wrongly because of these things. You don't know them, you don't know why they play the way they do, you can only make an assumption, and I don't like judging people so harshly based on how many mobs they pull in a dungeon.
I believe that if you find the party members to not be working out for your playstyle and you don't want to deal with it, then by all means leave. But I think it's also okay for them to consider it an unnecessary thing to be fussed about as its casual content, I just don't think it's cool to act in any way that dismisses people and how they play and make arbitary numbers on when they think they should have been good enough to know better, ex 'If you are in Endwalker you should know by now how to play your job' etc. I feel like all of this should have a bit more merit if this person suddenly entered, idk, savage? I would find it funny still but at least in that case you could genuinely ask them to maybe figure out how to play their job properly and learn what mitigations are.
i feel like my words are mostly resorting to sounding like "we should all get along" so it kind of sounds a little naive, but I believe the best player etiquette is to always try to communicate first before having any immediate expectations because you truly never know what's going on with your party members when you're in queue with total strangers.