I think you're selling Mac a bit short there. He was spot on with his assessment post fight, you can't be inactive and hang with high level guys. He missed with lefts that I've never seen him miss before and even the few times he caught Dustin, they were off the mark. Dustin was cognizant of Mcgregor's "pull" and still fell into it 5-6 times. A sharp McGregor doesn't miss those opportunities.
I think the mistake was in fighting a can like Cowboy and then taking a year off. If you're going to fight a can, fight a few until you're sharp. There were a few guys at lightweight that were big enough names but not very threatening for him to build off of. Felder, RDA, Barboza. Guys past their best before date, but with enough name value (and still high enough in the rankings) for the fight to look like it means something. Conor was clearly not ready for an elite fighter in there tonight.