Great, bad and everything in between is always going to be in every mmo because every human is different. That is why this happens. Just because you can do something doesn't mean everyone else is in a position to or even wants to.
And no it's not due to the absence of parsers. I met plenty of bad players in WoW who had parsers. They didn't feel magically inspired to do their best, they just did the bare minimum that gave them a quiet life. Which sometimes wasn't enough in top tier content, and obviously it caused problems.
There is no mystical cure-all when it comes to lazy or bad players. They will always be around no matter how sophisticated and freely available parsing becomes. WoW is a prime example of this fact.
Well no, they're not. Average players play just fine. I mean, this is why they're called average. Not amazing but certainly acceptable.