I think the core problem people have is a lack of knowledge and a misunderstanding of how to play their role. Take the person struggling with the lvl 99 dungeon for example. You can point at all the faults they have like scuffed hotbars, slow reaction time, bad rotation, etc but what truly prevented them from clearing is a faulty understanding what to prioritize and a complete misconception how fights in this game are designed. They thought as a healer they should stand as far away from the boss as possible and that the melee zone is very dangerous. This is based on absolutely nothing and if you asked them why they thought that you only got vague nonsense back, in essence a lack of understanding that standing close to the boss often gives you the best oppurtunity to dodge in any direction since melees generally need to have the chance to get to safe spots aswell.