Thats still completely ignoring any postseason success, which most here will agree is insanely important for a players legacy.
If you're counting the number of Stanley Cups won? Yes, agreed.
But McDavid has already led the playoffs in scoring twice. A few of the players on that list never even did it once (Clarke, Jagr, Ovechkin). Several more did that only one time (Beliveau, Hull, Mikita, Messier, Crosby). A few match McDavid (Richard, Lemieux). Only a small handful have exceeded what McDavid did (Gretzky, Howe, Lafleur, Esposito). By this method, McDavid is already tied for #4 on the list. Plus he has a Conn Smythe. Only three players on the list (Gretzky, Lemieux and Crosby) have more (though some of them - like Beliveau - probably would have won multiple Conn Smythe's, had that trophy been around for their entire careers). The only player ahead of McDavid on both lists is Gretzky.
Ultimately, I think you and I are in agreement. McDavid has only played in 74 playoff games, and I want to see more longevity from him. But if he maintains this level of performance, I don't particularly care if he wins a Stanley Cup.