Jose Aldo is able to make weight at 135 during an era where IV's are banned, while Conor was able to put on so much mass, that he had to cut down to make welterweight, that should tell you enough about the size difference.
If you can make the weight you can fight in the weight class.
100% man, no disputing that. It's an advantage though to be the bigger man and that was the case for Conor's best wins/best opponents (pound for pound).
Conor legitimately earned the FW title shot even if you hate him you have to admit that. He beat Mendes - a wrestler and top FW at the time - fair and square. He didn't look great against a wrestler at that time, but he won. Then he flat-lined Aldo in like 5 seconds. It is what it is, McGregor didn't defend any titles but his FW run is one of the best title runs in UFC/MMA history easily.
It is one of the best runs there, and yeah, he beat Mendes fair and square, but if i remember correctly, Mendes had like 1 week of training camp, and as mentioned: Conor was the bigger man, which is a big advantage when going up against someone who's known for his wrestling.
His stoppage of Aldo (despite the difference in size) was remarkable, i'll acknowledge that.
He dethroned a top PFP GOAT, and the clear FW GOAT, and he starched him.
Yes, he did so.
On top of that in general McGregor's resume' to this point easily shits on Justin Gathje's, Tony Ferguson's, or even Khabib's. Easily.
Nope, it doesn't.
Name-wise, yes, but not if you look at the context of these fights.
- Aldo: great win, despite the size difference.
- Mendes: good win, although the difference in size most likely tipped the outcome in favour of Conor.
- Alvarez: very good win.
- Cerrone: had 49 pro fights back then, took lots of damage, especially against T-Ferg and Gaethje. Also came off two losses.
- Diaz: With all due respect, but Diaz has lost a third of his pro fights at that time.
- Poirier: young and not nearly as good as he is now.
- Holloway: very young and just like Poirier not as good as he is now.
Khabib on the other hand, is 12-0 inside the UFC, with all these wins being at lightweight, against opponents his size - all of whom he made look like they didn't belong in the cage with him, with the exception of Tibau.
Ferguson, while less dominant than Khabib, also is riding a 12 fight winning streak at lightweight, with 9 of these 12 wins coming by finish.