How exactly are players going to get better in group content if even the lowest level of group content is going to get them harshly judged like they just entered a progression premade? You're looking at pug content like its the endgame- it isn't, it's the first steps. There's players that are going to hit their potential, and it might not be high, and they might not ever rise above pug content... which is why they're in pug content. I get why when players try to enter premades without any effort to get carried they'll get chewed out- but when you're entering pug content that's partly there to teach, and partly there to help people gear up, and you're surprised that people aren't geared up and haven't mastered their class?
The majority of the playerbase for any MMO is going to be well below those that do progression content, look up guides/strategies and keep up to date with patch changes- and that's fine, these are games and the casual content is going to be meant for them. Getting mad at average players for being average is an effort in futility and displays a pretty widespread ignorance of what games are. At no point was 'being the best' a requirement for playing games, you can all be as mad as you want about that but you're basically old man yells at cloud material right now.
The better question is- why don't FFXIV elitists do what other mmorpg elitists do and make their own premades so they can shun the casuals they hate so much? Casuals in FFXIV are no different from casuals anywhere else, just wanting to play the game and have fun- so it's kind of comical that elitists here are elite enough to look down on everyone else but not elite enough to put in the effort to min max their play and form a premade.
Which begs the question- you know full well that an optimized premade is going to be, oh how did you put it again... oh right 'good enough to know you've done your best' with? Why settle for a pug that's 'good enough to clear', why not bring your A game and go all out in getting that perfect comp of top notch players. Funny, you seem to have no problem looking down at everyone else who isn't putting in the time and effort to be the best they possibly can, but you're blatantly ignoring the biggest factor of group content- the group.
Let me guess- too much effort and time to make a group that'll be 'good enough to know you've done your best' isn't it?