For me the thing was Conor looked sicker, shittier than any fighter I have ever seen in MMA when he performed at 189. We can talk about who had more of an advantage, and sure, Chad would have likely performed better if he had a full camp but on fight night, Conor looked 10000 times worse.
That being said, any wrestler slows down after 2-3 hard rounds and what was so impressive was Conor's mental game; he didn't become gun shy, broken or tentative like every other fighter that we have seen spend two rounds on their back. Like Luke Thomas said, you never see a fighter charge the wrestler/takedown artist after spending two rounds on their back. Heck, look at his teammates Artem and Gunni, after Ryan Hall and Maya had them down down for just 1 round; it was as if they completely forgot how to strike and went into defensive shells. It is easy to say "what is a takendown or 2 or 3 in a fight to the death" but Conor really believes it and proved it.
There are countless examples, JDS vs Cain 2,3, BJ vs GSP 2, GSP vs anyone really, Vitor vs anyone that made it outta round 1 with him, Cormier vs Rumble, etc, etc. Being on your back makes 99.9% of fighters desperate; makes them work extra hard, blow their load and mentally and physically exhausts them. Conor really showed how mentally strong he was and what a true anomaly he is as a fighter (the type of fighter BJ Penn believed BJ Penn wasl i.e. "to the death Georges"). Even if Chad had him down for 1-2 more rounds, we saw no signs of mental fatigue in Conor and saw an incredibly efficient, yet consistently potent, fighter. It would be absurd for an Irish fighter (or any non wrestling based fighter) and his coach to expect that they would never get taken down in the UFC and everything Kav and Conor said before the fight shows that they painstakingly practiced efficiency on the bottom, maintaining mental acuity, presence of mind and awareness.
Also, the cookie cuts both ways. As I said, that was by far the worst, most sickly and weakest Conor will ever be and I have no reason to doubt that he was seriously banged up and ill as it was reported. At 194 he looked like a completely different animal; fresh, buoyant and healthy. A picture is worth a thousand word and the top pictured fighter is much farther from optimal operating levels than the bottom pictured fighter.