The Brewers major minor league pieces are offensive players. Them not tendering Schoop doesn't mean that they're not willing to trade their top prospect Hiura like everyone is claiming. The Brewers don't have a lot of minor league depth, but the depth they do are mostly blocked position wise in the OF and at the corners. The Brewers also have a lot of interesting trade chips on their major league roster like Corbin Burnes, Freddy Peralta, Orlando Arcia, and Domingo Santana that could attract a lot of interest from the Mets/Giants. It's not a clear cut thing, but I sense the Brewers understand their weakness to their club was SP, and that they have a plan to address it. As much as they were able to do last year, you can't rely on Wade Miley types for consistency.
If the Brewers offense regresses some, but they address their pitching, they're still a mid 90 win ball club. Also, as amazing as the story of the Brewers was last year, don't forget how shit their pitching health was and how inconsistent their offense was from early in the year.
Don't get carried away with delusions of how much better one player can make a team. The Yankees cummed themselves over Stanton and their bullpen last offseason and still weren't able to bridge the gap over a better Red Sox team who made just one key move to address a minor weakness. And the Brewers just feel one big name SP like MadBum or Syndergaard who can catalyze their rotation away from being a really complete team. And they had the best record in the NL without really finding their team identity until September.