I would never fully count out Sid, but the main issue right now is he seems to have a nagging injury every season that forces him to miss 10-15 games. His pace has still been really good, I think he would have been around 10th or so had he played all 82 last year.
That's only true for 2 out of the last 9 years.....the other 7 years his missed, on average, less than 3 games a year.
The answer to the question is pretty easily "yes" though. Pretty tough to expect 35+ year old Crosby to compete in a scoring race against a prime McDavid and a few others. He's holding his own very respectively....think he's 5th right now, but unless there are injuries, I just don't see it as possible.
St. Louis did it, but it was a short year and if Crosby didn't get hurt, all indications were that he would have won it in a landslide (like 25% ahead). That's the type of thing that would have to happen I think. That year, Kane wasn't quite there yet in his career, Malkin missed half the year, Ovechkin was scoring goals, but not really a scoring champ threat......you just didn't have the top guys quite in their prime the same way you do now, so it's extremely unlikely unless there are injuries.