You dont think the difference in cardio between the Alvarez and Diaz fights is that Mcgregor had a tough fights with Diaz and a ridiculously easy one with Alvarez? While I dont think Mcgregor has horrible cardio, but IMO it has absolutely nothing to do with what weight class he is in, its on how much energy he has to expend to maintain a level of pace to implement his volume pressuring style, based on the matchup he is faced with. The Diaz fights he had to unload on Nate to get any effect, Nate would give him a couple back in exchanges, McGregor really had to work hard to implement his game. Alvarez was in Conors world the entire fight, he was getting hurt and detered anytime McGregor landed a punch, McGregor maintained excellent positioning in the cage through the entire bout, landing anytime he threw with minimal effort while taking minimal shots himself.
EDIT: after perusing fightmetric, Over the first 2 rounds of both Diaz fights, Mcgregor threw approx x2 more strikes and received x8 more strikes when compared to the Alvarez bout. 2 of Eddies 9 total strikes were to McGregor's head.
We'll see if Khabib looks more like Nate or Eddie. But Khabib's chin, pressure and toughness leads me and many others to initially believe that Conor is going to have to work hard in this fight, and in that case putting stake in his historic gas tank issues is 100% justified. Conor's energy seems to be cyclical throughout the bout so he does recover, but he has very visibly gassed during moments in his tough fights.