I strongly disagree with this statement. Shaw was a consensus top 15-30 prospect in baseball coming out of the 2024 season with a 144 wRC+ across AA and AAA in his age 22 season. Caissie featured a 139 wRC+ at AAA in his age 22 season and Ballesteros had a 121 wRC+ in AAA in his age 21 season. Shaw also had the added benefit of being a plus defender at an infield position, which neither has.
This isn't to say that Caissie or Ballesteros won't be better hitters than Shaw in the majors over the course of all their careers, but it is a reminder that Shaw was a premium prospect at this time last year with a really good offensive and defensive profile. Caissie and Ballesteros could easily see similar struggles as Shaw did this past season, if not worse, in 2026. Whether penciling Caissie and/or Ballesteros into starting roles in 2026 is a good idea is a post all of its own, but I would not use their projected value as a basis for how Shaw should be used in 2026.
That said, while I've been slightly in favor of trading Shaw, if the Cubs end up keeping him, he's a pretty good bet to end up around the 3 fWAR range, which would make him a Top 10 3B in baseball. You can upgrade from him, but the position is basically a wasteland across the league and the options to do so are pretty much limited to Bregman, Bichette, and Suarez (unless you believe in one of the Japanese imports). Shaw's easily a starter on most teams.
However, even if Shaw is the everyday starter, he's going to need days off and injuries are always a possibility. BJ Murray is pretty much the only person on the farm who *could* man the bench role, but his ceiling is limited and he needs more development. There's currently no one on the roster who seems like they could be a competent backup, either.
Someone like Paul DeJong seems to make sense as someone who can handle 3B with a bit of pop, but yeah, this is a really thin crop if you're hunting for bench candidates.