Personally I also believe that the 'XIV players are bad' is largely attributable to individual complacency; when all a player does is expert roulettes and the occasional extreme trial, it can be easy to start thinking 'why strive to be the best when I don't need to?'. And I think it's an interesting question with no concrete answer; when you can get away with doing 'ok', at what point does doing 'well' become an impediment. You could try to hit every single proc, DoT every single enemy, use all your abilities a split second after they go off to ensure no procs are wasted and utilize your support abilities at the most opportune time. Or, you could just press buttons and still win. I know I'll get my throat slit for saying it, but I honestly believe that 'damage meters' have had at least some impact on this. Being able to see numerically the disparity between players give the impression that this large disparity is solely due to player skill level. In reality, there are countless extraneous variables that must be accounted for before conclusively saying 'this person is low skill and doesn't care'. A parser can't tell you what a person is thinking, their motivations or their limitations. And generally the player won't tell you either unless it's a friend or acquaintance (which doesn't help matters)
Imagine you've been playing FFXIV since ARR. You aren't familiar with what a 'parser' is (unlikely I know, but let's assume for the sake of argument) but you've managed to beat everything you've come across so far. You enter, say, expert roulette, and suddenly someone is calling you out for 'bad play', 'poor rotation', 'low dps', 'not enough APM'. You have no idea that this 'disparity' exists, and even if it does, if you've been able to beat things despite it then why are you doing bad?
The presence of damage meters has caused people to expect the disparity in dps to translate to disparity in skill at a 1:1 ratio. Furthermore, people generally seem to expect a much higher skill than necessary for most content because damage output can be converted into pure numerical data.
Does anyone even know what the absolute minimum amount of damage one can do before causing a wipe in non-savage content? If a Black Mage only does 2500 dps to your 5000, will it really matter when running Hells' Lid or The Fractal Continuum (HM)? I wouldn't imagine so.
Also, in an attempt to cast Palisade on myself, I'd like to point out that giving people friendly advice about more obvious mechanical mistakes (e.g Ice Mage, Healer Paladin, Bards with no songs, Summoner with Titan, etc) is completely fine. But saying things like 'you're doing 2000 dps but I'm doing 3000' does absolutely nothing to address the issue. You're literally just saying numbers with little context.
Unless parsers begin to access people's cameras to see how they're physically reacting to the game, the reality is that they don't give enough conclusive evidence to accurately state that there is a large disparity in player skill that is the result of lazy players who just don't care