Well, this opinion didn't just occur to me, Ive known for at least two seasons that he's somewhere along the lines of Crosby at the same age (I think Sid was a bit better from 18 to 21, remains to be seen for the rest.)
I think you may be jumping the gun on "best since Lemieux". That's still Sids to lose until he does some of the more amazing things, like two connies in a row, his ridiculous point streak, changes his game completely to fit his team (From speedy playmaking offensive-first, to goalscorer, to 2-way player.)
I also would like to point out that Malkin has a better peak than McDavid, so far.
What about Ovi's ridiculous stretch, too? From 07 to 2010, I think thats yet to be beaten by McD's too.