Crosby is one of those guys that gets every free pass in the book given to them. He didn’t even play half of Game 7 against Detroit during Pittsburgh’s first win and underperformed during each and every Finals appearance, but sure, let’s pretend he’s this SCF god.
As of today, Crosby has a legitimate case for #5 all-time. There are several players who are in contention for that spot, but he might have a stronger case than anybody else. (I fully expect McDavid will pass him, sooner or later).
But one thing that's always bugged me about Crosby's resume is underwhelming numbers in the Stanley Cup finals. 20 points in 25 games is, frankly, disappointing for a player of his calibre. Most of the other top ~20 forwards look better (Gretzky, Lemieux, Howe, Beliveau, Hull, Lafleur, Trottier, Bossy, Messier, Clarke, Mikita, Sakic, etc.) scored at a higher rate, with many of them being substantially higher. The same is true of some of his peers (even if Crosby is a better playoff performer overall - Ovechkin, Kane, Kucherov, Zetterberg, etc).
There are a few counter-arguments - 25 games is a small sample size. He was a good two-way player. And this was during a lower scoring era than today. All those points are valid - but I don't know if that explains such weak output.
Even with this weakness, Crosby is still probably the top playoff performer of the post-lockout era, and he's arguably #5 all-time (until McDavid most likely passes him). But this is a legit weakness in his resume.