Why does it need to be all on Jack? Our secondary scoring was horrendous last year. A 40 point jump in the entire bottom 9 is a completely reasonable thing to expect, even if Jack ends up missing 20 games and ends up around 60 points again.
It doesn't. But, the improvement of the Avs and Devils last year was driven largely by the massive jump in production that you saw from Hall and MacKinnon.
If you were to expect the Sabres to have a jump like that, then maybe you need to see some of the same things happen, like Eichel having a big step forward.
I think the the Sabres will need three main things to happen to move forward next season:
1) Housley and his coaching staff need to be a lot better
2) Hutton and Ullmark need to be a lot better than Lehner/Johnson were last year
3) They need much better play up and down the lineup at ES
If they are jumping from DFL to playoff contention, then I think they also need Eichel and Reinhart to have a big step up in production and Dahlin and Middlestadt need to have All-Rookie Team seasons.
I think enough of those things will happen that they are better. But, I don't expect enough of them to happen such that they are in the playoff mix in 2018-19.