Listen, there are level 70 healers standing still and only casting if someone is not topped up. That's not a matter of being bad at the game, that's laziness. You can be awful at the game and even some of the worst tanks I've seen would usually get better when they tried. Dungeons (that are not Criterion!) are content that require zero, and I mean zero skill. A literal 12-year-old could do most of them. You get drip fed easy mechanics from level 1 to 50, by 60 you should know most basics. By 70 you should absolutely be able to know most basic shit, and refusal to do so is honestly just expecting others to carry you through content. Hell, I am godawful at AST but I still press more buttons than round 4 of "oh but my primary job is healing" Andy who doesn't wanna weave after a GCD even though they made everything have a weave slot.