I understand the main concept that you are presenting here.
But you are comparing Dionne/Perreault with Risebrough/Jarvis. Hall-of-Famers with 3rd-liners. Apples-to-oranges.
This thread is about McDavid's legacy. The thread title states "legacy".
This normally translates to "All time standing".
So, instead of comparing apples-to-oranges, compare apples-to-apples.
Compare McDavid to Crosby, for example.
Similar to how Marcel Dionne and Gilbert Perreault will never be held in as high regard as Guy Lafleur, I don't think McDavid will ever be held in as high regard as Crosby if McDavid can't ever win the Stanley Cup.
He doesn't have to win it this year. If he loses it this year again, people won't necessarily hold it against him as long as he can win it some year.
But if he finishes with 0 Stanley Cups? Then yes, his legacy suffers when comparing him against other all-time greats.
And I think that is fair, since all the legends and all-time greats before him were also judged by whether they won the Stanley Cup or not.
Crosby, Ovechkin, Lemieux, Gretzky, etc. They were all judged differently before they won the Stanley Cup. They all needed that Stanley Cup win to cement their legacy. Why make different rules for McDavid?