Certainly his games missed is the main limitation to his career, yes, but I wouldn't say "that's it" keeping him from top-5 status. I mean, what has Crosby done that Beliveau, Lafleur, Esposito, Hasek, or Lidstrom didn't do?
I think it's a safe bet that Crosby would have had nine straight 100+ point seasons if not for injuries, from his rookie year through to his last scoring title, 2013-14. That's incredible in his era, and (would have been) a major feather in his cap. (But it's not even that amazing -- we could say the same of Peter Forsberg, in an even lower-scoring period.)
Besides the injuries, I think there are a couple of points about Crosby's resume that are a little -- I'm not saying "a lot" -- limiting to his chances of hitting the top-5, which, to be honest, is a ship that I think has long since sailed. One is his notable scoring decline from age 27 onward. It's not unusual for players to do so from, say, the late-20s, and Crosby of course has still been 'up there' near the top. But from age 27 through 31 (five seasons), he's third in PPG, and basically interchangeable with Kane, Kucherov, and his teammate, Malkin -- all fantastic players of their era, but none anywhere near the top 40 or 50. (This wouldn't matter a lot if Crosby's earlier peak had been played in full or been eye-poppingly dominant for long sustained periods, but it wasn't.) The second point that I think slightly limits him is that although he was superb in the '08, '09 (although even then the Pens won game 7 in '09 with him sidelined), and shorter '10 playoffs, he was kind of mediocre for years afterwards. From 2012 to 2016, his playoff stats are 54 points in 62 games, with a minus 11 rating. If this is happening now, I'd give him a pass, but this was right in the center of his prime years and includes a Stanley Cup team. Fortunately, he bounced back strongly with great performances in '17 and '18 (but then another no-show in '19).
I personally think the player with the best case for #5 in all-time rankings is Dominik Hasek, but whatever. A year ago, this board voted Crosby #12 all time, and though I don't vote on such things, I'd guess that's about right. He'd be higher, for sure, if he hadn't been seriously injured a few times, but #5...? I don't really see it. Of course, we're into speculation then, and we'll never know what would have happened.