Did you not see him rip up the Stanley Cup Playoffs en route to a Cup a year and a half ago? He just needed to get healthy enough to play a full season. It's not like the whole thing with the neck surgery wasn't well publicized.
I think it was more just about finding his game again and adjusting to a new team more than it was health, in his case. He was (barely) sub-ppg for the first 90+ games upon his return, and I think at first it was just getting on the ice, feeling ok, getting the game speed back.. then he slowly added the shit that makes him special, holding the puck and having dudes bounce off him as he circles about, and boom- he’s back to his peak. Totally different team and culture to adjust to, I just don’t think he was in a rush to put the team on his back until he had/has to.
Also, his highs in Buffalo were underrated. Dude went all out for 25+ games for us (playoff-sorta intensity) and that not resulting in playoffs mighta broken him. I just remember like a 3-2 win in Ottawa where it was just a Jack hat trick, then the next game we lost 4-2 with 2 Eichel goals or somethin, shit like that. I remember him thoroughly outplaying Matthews in at least one matchup. He’d have potentially hit 100 points with one decent linemate when he was at his best, but alas, not to be. I think he’ll age really well, health and a decent squad were the limiting factors for him in the past.