every time an MMO community obsesses over this concept we get an expansion where the entire endgame is for the ultra-hardcore audience and everyone hates it.
the issue isn't casualization.

the issue is that you, like anyone else, are playing a game that takes a small but not insignificant amount of skill and when given enough time (such as when playing an MMO, something you do potentially for years) will improve at said skill and so all new content will seem "easier"; especially when they standardize certain mechanics like AoE markers.

instead of the catastrophe we had during the HW days where AoE/Stack markers had zero consistency, we now have mechanics that an experienced player could probably resolve or at least minimize DPS downtime/vuln stacks as they figure it out.

additionally a lot of the people complaining about the game becoming too casual are also the ones that use addons to tell them what to do so of course it's going to seem easier when you have a voice barking commands at you while your combo and procs are all consolidated into a single button.