I'm an old school guy too, but sometimes we romanticize our old favorites a bit too much. BJ did have a granite chin at LW, no question. His bjj was obviously terrific, how he got his nickname, etc. for winning the Mundials after so little training. His TDD was stellar for sure, but his offensive wrestling really was extremely average (if that). His boxing was very good too, among the best in the sport in his prime. But he had zero kicking game, wasn't even a threat with it. He did find a variety of ways to counter really good wrestlers (the flying knee to Sherk as Sherk tried to level change was a thing of beauty).
But...
Conor manipulates distance so much better than anyone BJ ever fought. He combines precision and power better too (Machida maybe being the one guy you'd compare). Conor also has a granite chin. I'd give prime BJ the cardio edge though.
Prime BJ vs Prime Conor at LW would be stylistically one of the more fun hypothetical fights to make. I just think it's over-the-top to say prime BJ "murders" Conor.
The current LW division is just insanely good though. Unbelievably good. Conor is probably the 3rd best LW in the world right now imo. I think he loses to Khabib, but I think Ferguson is actually the best LW on the planet. Plus you have Poirier, Gaethje, Alvarez, etc. AND the younger guys like Gillespie coming on to the scene. If you rule the LW division in this era, you are special.