It's not about their ability to score. They rely on goaltending because a goaltender is their best player.
When the Jets get into the playoffs, Mark Scheifele has to match up against Nathan MacKinnon, Connor McDavid, Jack Eichel, Anze Kopitar. If they get to the Finals, it's gonna Barkov, Matthews, Hughes. When the other team is sending their best after your best for 7 games, it becomes difficult. That's why teams with top, top talent bogart the Cup. They're in a 1v1 matchup with him and they're gonna be trying to stop him. They can keep the puck away from him.
The other goaltender doesn't have to beat Hellebuyck 1v1. His performance is independent of what Hellebuyck doing. Hellebuyck can't directly stop him.
Because of that, the mismatch for Winnipeg in goal is providing nowhere near the value of the mismatch they're going to be facing at center.
It's hard to win a series when your top talent is a goaltender and he isn't providing a 1v1 matchup advantage.