I think the oversimplification of the game is a much bigger problem than people unsyncing content.
Yes, the casual content was always easy. But in the past, playing your job and playing your role were both slightly more complex. Now that the jobs are incredibly similar & simplistic and role responsibility has been degraded to the point that you barely need a tank or healer and enmity isn't an issue in any way, you don't really need to pay attention. You can just AFK through most normal mode content.
It shouldn't be a surprise that people end up being terrible at the game when the game does everything it can to teach them that they don't need to pay attention and their performance doesn't matter.