While I don't think McGregor is the best fighter in the history of the UFC and is no GSP everyone saying he is a bum and terrible is off their rocker. He has beaten everyone the UFC has put in front of him, beat a guy that was considered one of the best pound for pound fighters in Aldo, went up TWO weight classes to fight a legitimate contender in Diaz, kicked his ass for the entire first round, then got tired and choked out. All his wins were a fluke or there were short camps, or they weren't good, etc yet he loses to a guy 2 weight classes above him and that's legit? He didn't get a full camp to add 25 lbs of muscle, he just didn't have to cut very much.
Who else has done all of that? And he's made millions for himself and for other fighters including the UFC. I was glad to see him lose even though I didn't think he would (to Diaz). His ground game has holes but if no one ever gets him down, who cares? Mendes had him down a lot, he came back and won. Chuck Liddel didn't have a very good ground game, so he worked on his take down defense. That's what I would do as well.
He's really good for the sport. I hope he continues to fight, win or lose. No he's not the overall best fighter ever, not yet.