I honestly don't consider the people that afk on limsa everyday and feel entitled to every single reward with barebones participation are casuals. Casual players are people that don't give a lot of hours to the game and that don't engage in a lot of endgame activities like savage or ultimate, not players that stay subbed and online everyday but have zero interest in any gameplay or learning curve. That is an entirely different crowd. Like these people breath FFXIV, barely play other games, even raiders that log in two days a week are more casual than them.
That being said, I feel like someone being bad in a group making your life miserable is sort of dramatic.
IMO while we have more and more people that are simply lazy to commit any time at all to something, the game gives you zero reason to actually feel like you have to learn your class.
First of all, most classes feels barebones if you are not at the level cap and there is few or next to nothing repeatable daily content where you are actually at level 90.
Most content normal content can be cleared without asking for your full kit.
Without third party tools you actually have NOTHING to tell you if you are doing it right or wrong, if you are being able to do a good amount of damage or not, so many people do not even realize they are terrible.
And lastly, getting better at your class is not an exciting journey in this game. You rarely feel like you are making a difference by being good, there is only so much you can do, and once you are "good" there is... nowhere to go, really. You can't put your twist, you can't customize, you can't find your way of doing something. So most people lose interest.
In general, the game rarely strikes your curiosity... You can keep on being mediocre and unless you are curious and go for that information, nothing you make you sparkle "hey, how should I be doing x?".
So yeah, I don't really blame people for not even trying to be better at the game because being better makes no difference. It makes no difference to your gameplay, to the fight you are doing, to the way you use your class.