I've had my fair share of people who refuse to pull their own weight for whatever reason (or otherwise intentionally fail at their job), but I've also seen a fair amount of people that go "well I don't want to put too much effort, they're dying and it's easy".
To rebute that; it's supposed to be a game. Nothing in this should be that mentally taxing (excluding A3S savage, but this was expert roulette and everyone was at least law+ gear) that you can't be bothered to incorporate it into your playstyle. It doesn't even just apply to games (but it's certainly the lowest common denominator imo if you can't even be bothered to put effort into that) but life in general; you don't want Jimmy slacking off and his co-workers doing all the work, if not more to compensate.
A pletoria of people exist, including the ones mentioned in the last few posts (and those especially special ones that queue as a group for CT just to mess with the other two alliances). Whether or not you want to put up with it (and if you can do anything about it outside of GM influence) is another thing. In regards to these people, it's not even a matter of "git gud", it's a "stop sandbagging" because for all intents and purposes, they can play better but willingly choose not to (versus the common context of "git gud" is literally to "get over it", especially if it's in context of job changes).
Just stop taking what we say to the extreme end and hopefully you can see the perspective on this. We're not even iffed at people playing that aren't playing "to our standards" (unless again, you want to take that to the logical extreme where our standards is "giving a shite about the dungeon",) but having the courtsey of doing whats expected of their job and following the fundamentals.
And just to repeat what I've said before.
It's not about subperforming because they aren't good at the job, it's those who can do better but willing choose not to out of spite or laziness (in a game setting). This means people who do DK>TS>SP combos as a MNK (and drop greased lightning somehow) and still do less than the tank on average, not AoE on trash (both of these in perspective of the latter), or ice mages (in the case of the former)