I agree with both of you actually, while disagreeing with both of you if that makes any sense.
It is and it isn't.
It would be the greatest achievement in the history of the UFC by default, no one has ever done that. No one has won a title across 3 divisions.
But it also in reality and context wouldn't be because McGregor would essentially be gifted a title shot against the weakest / most winnable opponent possible at 170 for no real, merit based reason.
I definitely think him beating Alvarez was totally legit. I'm sure you disagree, but he dominated 145, dethroned a GOAT, and was a huge draw. RDA dropped out, he split with Diaz at 170 (a LW/WW tweener) after coming straight from FW. Then he destroyed Alvarez, who was a legit champ and a wrestler, we can't revise history to say that was an easy match-up.
If Masvidal wins, he would legit be champ as well. But McGregor really has no claim to fight at 170 for a title, it would be purely on popularity/$$$ and based on one win over a ~top 10 guy who is also a LW/WW tweener (Cerrone) but was competing as a LW. However, the arguments were that McGregor doesn't deserve a LW win based off that from many...so it would also be ironically hypocritical.