No, it isn't. In sports, plenty of generational players started their careers relatively slowly and were not considered elite at age 19 (Jordan, Djokovic, Tom Brady etc). In hockey, there are many elite players like this as well (Joe Thornton, Jagr, Iginla, Messier who was 2nd round draft pick, etc etc).
Gordie Howe also exists and was a generational player, even though he didn't start dominating offensively until much later.
Wait and see is the only correct answer.
We're talking hockey, not the other sports. All the other "generational" NHL players came on strong immediately. Of course, it also comes down to who one considers "generational", and for me it's a short list.
Since 1970: Orr, Gretzky, Lemieux, Crosby, Ovechkin and McDavid. - All of these players dominated from the very start of their careers.
They are the clear top 1 or 2 players of the era in which they played.
Of course, Howe is as well, but the game in the 1940s can't be compared to the game today so I leave him out and keep it to the modern era.
If we want to compare Bedard to the other players you listed (Jagr, Thornton, Messier, etc.) that's fine. And it's probably more likely that Bedard falls into a group like them (ie Kane, Kucherov, Datsyuk, MacKinnon, etc.) But I don't consider them the 1 or 2 top players over an extended period of time when they played. They were all playing in the shadow of a greater player of their era.
The OP says Bedard is the next Crosby or McDavid. If he is, then we need to see it because Crosby and McDavid showed us in their first two seasons.
'Generational' is a made up term of art in the sporting context. It doesn't actually mean anything, people spend way too much time debating it.
This is true. But this is a forum where stuff like this is debated.