Ovechkin is the best goal-scorer ever and arguably the best LW ever (the memory of Bobby Hull is beginning to fade, so Ovechkin as the best LW ever will get more and more traction)
This is something that is hard to match; just like Jagr's 4 Art Rosses in a row, the more time passes and no one comes close, the greater the respect for Ovechkin is going to be
Ovechkin also has a very high, clearly pronounced peak of three consecutive seasons. I am not sure, for example, McDavid has three consecutive seasons to match Ovechkin's 2007-2010. And again, the longer passes before anyone matches Ovechkin peak, the more impressive it is going to be.
On the other hand, the blemishes in Ovechkin's resume will look more and more petty. For the future generations of fans, Ovechkin will be a Conn Smythe winner, who won the first Cup for his franchise and led his era in PO goals. They will be much less receptive to stories of Caps PO struggles, just like no one holds early-career PO struggles of Yzerman and Datsyuk against them. Likewise, all the silly complaints about Ovechkin's down seasons will end, just like no one remembers any longer Hull's and Howe's under-ppg seasons, and even the memories of Jagr's Washington stint are beginning to fade.
Crosby's legend has very little growth potential, since he is not close to being the best ever in anything. There is nothing in his career for the next generations to look at and be amazed. Three Lindsays? McDavid has matched that already. Two Art Rosses? Duh. Three Cups in the salary-cap era? Toews and Kane also have three, Kucherov and Stamkos and Vasi may well join them. Crosby is likely to be overshadowed by McDavid; more prolific scorers will likely come.
In a sense, Crosby's legend is already beginning to fade - as much as Crosby was pumped to be 1B to Ovechkin's 1A in 2007-2010, no one is buying that any longer. Back in 2007-2010, many folks drank the media cool-aid and bought in "the rivalry" NHL was trying to sell. Now pretty much everyone realizes that in 2007-2010 Ovechkin was just better.