In a game where you can spam a completely no-skill dungeon (POTD) to get to at least 60, where are we expecting people to learn? The game needs to press its players more to challenge them and get them up to snuff. There should be basic checkpoints along the leveling curve to make sure you're meeting at least a minimum standard. Like a class quest for DPS where you get your gear and level synced, and have to hit X DPS within Y time to pass. And the only way to do it is to understand your cooldowns and, if applicable, positional moves. Nothing crazy, it wouldn't have to ensure that you could be maximally efficient. That kind of skill is something those who want it should be seeking on their own. But at least enough to where if you dropped them in a dungeon, they'd know what all their abilities are for and generally when to use them. There could be one for healing where you're simply tested on your single targets vs AOE vs instants alongside cooldowns, and a tank one where you hit a wall and watch paint dry because you're not allowed to move or have fun!
These wouldn't have to be hard or confusing affairs. The game could straight up come out and tell you what abilities to use, that's fine. It's not a pride check, it'd be there to make sure you're confident and capable. And if you spaced them out just right, you could go from learning how a super basic combo works at level 10, to properly weaving in your cooldowns, placing your debuffs, etc at 70. Maybe give a little title, minion or even mount for taking the "mastery exam" or whatever. Reward people after teaching them. Reinforce the good stuff. Not everyone's equally motivated to learn on their own, and generally if they've irritated someone enough to say something about it, what they're gonna say is rarely very nice, and if it's not nice, the basic human response is to get defensive and dig in your heels, because we're just dumb animals. This is totally solvable with game design.