I think one of the main reasons for people that don't play their class as intended is that they try to play this MMO like they would play others. Healers in this game aren't full healing machines and their DPS is actually not bad at all, and Tanks are supposed to always be rotating cooldowns, not "oh look I'm almost dead, better pop Rampart". But I think that the two biggest problems are the difficulty curve of and its effect on inexperienced players.
Pre-50 and even the majority of lv 50 dungeons don't really offer a challenge. Many tanks don't learn how to correctly cycle between cooldowns because WHMs/SCHs are just panic healing every time their HP goes under 95%, and many healers resort to panic/full time healing because tanks are not mitigating correctly; it's a vicious cycle. Then we have DPS players who either refuse to or do not know their correct rotation because bad player mentality is "it doesn't matter as long as we get the kill". Good DPS is not a nice thing you do for a group, it's your job.Then there are also FATEs, which teach you absolutely nothing about your class. This game offers no worthwhile challenge until Tanks do Garuda HM and DPS/Healers do Titan HM, and this too is now void with the Echo buff.
I remember the first time I did Titan HM in 2.0, it kicked my ass and it felt GREAT. I studied the fight and spent an entire day making PF groups that would wipe endlessly until I finally made one that got the kill. Seeing that Stardust Rod on my back made me giddy for hours. A lot of new players used to complain about Titan HM being a roadblock, but that's exactly what it's supposed to be, because back then, when players didn't have such good gear, you either got a good grasp on your DPS rotation or you'd have a hell of a time burning the heart.
Now we have much better gear and the Echo buff. The main problem I see with the Echo buff is that it once again encourages mediocrity. Bad players don't need to get better because they do the same damage with 40% Echo that a good or even decent group does WITHOUT Echo (I'm not even exaggerating, I've been doing Titan HM this week countless times to help my friend farm for his Titan staff). The problem with this is that an endgame fight that originally made you reevaluate the way you play is now "smash your head repeatedly until you get the win with a 50% handicap". Now you can do HM Primals without learning the fights, and then unlock EX Primals (good luck with that). I understand that a lot of players just want to see content and some do not feel like learning a fight, but the problem with this is that this is a team game. If this were a single player game, you could play however you wanted because it's not affecting anyone. But when you play with people, and you are not doing your best, then you are holding everyone back and affecting the whole group.
I understand the point of the Echo, but I see it as doing more harm to the community than good. If you cannot beat the simpler fight without the Echo, then you cannot expect to perform adequately on the harder fight that follows.