For a long, long time into the future, Ovechkin will be a player young stars will be compared to - and repeatedly fall short.
Every time a new big-time goal-scorer will come into the league, people will be saying "is he as good as Ovechkin though?"
Every time someone will post a 60-goal season or otherwise a really dominant season, people will be saying "how does that season compare to 2007/08 season by Ovechkin?"
Every time we will see someone establish himself as the best LW of the past 5 seasons or the best goal-scoring winger of a decade, we will be asking "what does this guy have to do to come close to Ovechkin?"
Ovechkin is such a convenient benchmark: he has a strong identity, so we know who is similar to Ovechkin and who is not, he has well-pronounced achievements (peak play, goal-scoring titles) to compare to, and he is also not Gretzky, people will not roll eyes at the comparison from the get-go.
Ovechkin is also a recent player: probably it makes sense to compare a future star LW to Lindsay before we compare him to Ovechkin, but who saw Lindsay play? Even now, very few folks did, and 20 years from now the answer may well be nobody. And even those who did not see peak Ovechkin play have Youtube full of Ovechkin videos at their disposal.
And then, as we compare a generation after a generation of future stars to Ovechkin and nobody quite measures up, we will begin to understand what kind of player Ovechkin was.
As for Crosby as a benchmark: why not compare future stars to McDavid or Malkin? Or, if they are goal-scoring centers, one can compare their goal-scoring to Stamkos. Or, if they are pass-first centers, we can compare them to Thornton or Forsberg. Or, if they are good at defense, we have Bergeron and Datsyuk and Sakic as benchmarks. Crosby lacks a strong identity, he is not historically good at anything in particular, so as time passes, he will merge with the big crowd of award-winning, all-time-great centers.