Crosby's prime was mostly robbed by injuries. I think if you have him playing full seasons in his prime years he probably has at least another 2 Art Rosses (2010 and 2012 come to mind) and he would have had a shot in 07-8 (Ovie won with 112 points, Sid was on pace for around that), and 2011 (Malkin won with 109...Sid probably ends up with around there if he played).
07-8 and 2011 are much bigger what ifs while 2010 and 2012 looked like guarantees (2010 was the insane 25 game point streak and 2012 had him losing the art ross by only 4 points despite playing 12 less games than MSL).
McDavid thankfully has had a healthy career for the most part so far but even putting that aside the fact that he has 5 Art Rosses and with potentially more still on the way....it's pretty indisputable that he's had a better regular season career than has Sid. The only real edge Sid has on him is rockets but even there Sid only edges him by one Rocket.
I'm a Pens fan btw. But for me it's pretty inarguable that McDavid has had the better regular season career than Sid. That's just a fact. Anyone who wants to argue otherwise is being a homer. McDavid is the greatest talent to enter the league since Mario.
That doesn't diminish anything Sid has done though. 3 cups, 2 Smythes. McDavid is going to get judged by his playoff success (or lackthereof) even if it's not fair to do so given the playoffs are a team game. If McDavid ends up winning even one cup I think most people will comfortably put him ahead of Sid. If he wins two there's no question. If he doesn't manage to win one....he arguably still deserves to be considered a better player simply by virtue of how insanely good he's been individually, but people will hold the lack of playoff success against him.