LeBron destroyed Kobe at 19.
Kobe Bryant was scoring 81 points and winning championships when LeBron was in his first couple of years.
He was close in ability though, but that's the same as McDavid.
You can put McDavid on the same ice with Crosby and Malkin and he can play as well as them on any given night, for example in the Oilers-Penguins game, McDavid was clearly the best player on the ice.
I'm sure Mario could do the same against Gretzky early on in his career.
But consistently and peak level performance, that doesn't happen until you get further into your 20s, part and parcel because experience and strength develops as a talented player gets further into their 20s ... they can score more and do more impressive things because they know all the little tricks and develop greater efficiency.
McDavid at age 25/26/27/28 is going to be a lot better than the player you see now, who is already an amazing player.