Well, one interesting part of this trade rumor is that Miami was reportedly looking at sending Luzardo to KC for a young first baseman (Pasquantino), not pitching prospects, and at least one source suggested (though it wasn't as clear elsewhere) that KC was the one to back out. So potentially Miami is one team that might trade a young pitcher with the primary return being young hitting. Since Casas is probably more valuable than Pasquatino, the Sox might also be able to pick up extra pieces as well.
Obviously, the risk of trading Casas is that he becomes something like the 1b equivalent of Juan Soto (MVP bat with a bad glove), but how likely is that? He looked that good in July but it seems more likely that he ends up (and I would think this is a reasonably optimistic estimate) something more similar to how he looked in his minor league career (374 OBP / 859 OPS). That's a damn good player, but it's essentially a LH equivalent of Rhys Hoskins, who actually looked a lot better than that (with the bat) in his first season (1014 OPS).
I guess my point is that 1b/DH types that can give you an .850 OPS might be more replaceable through lower risk contracts to aging players than ace talent starting pitchers. I mean, who is the Rhys Hoskins of the pitching market this season? Seth Lugo, maybe? In other words, signing a 30-year old Rhys Hoskins to fulfill that function (eventually, replacing him with someone else) is much easier than finding a pitcher of any age that would be the pitching equivalent of Luzardo: i.e a starter with ace caliber potential. Also, with injury risk considered, wouldn't you rather rely on younger (but somewhat established) pitching and older hitters, than younger hitters and the type of older starters that you can get on low risk deals? In other words, isn't it more likely that Rhys Hoskins is going to give you Casas production than Seth Lugo is going to give you Luzardo production? I think this is a pretty arguable case, especially when you are talking about a player like Casas who brings nothing to the team other than his bat (i.e. a 1b/DH type).
Oh, just to be clear, I think there is a clear line of demarcation between trading hitting PROSPECTS for MLB pitching and young MLB hitters for pitching. The former, I think is going to be incredibly difficult unless you're talking about someone being a top 10ish prospect and performing very well at the upper levels of the minors.
Or - put another way - I think the Marlins would absolutely deal Luzardo for Casas (and I don't think the Sox should - mostly because of Luzardo's injury history). I also think the Sox would trade Mayer and Bleis or Yorke for Luzardo and Miami wouldn't consider it.
Statistically, per WARP, Luzardo is behind Bello, who many here think is a mid rotation starter at best. Luzardo is also older than Bello. This doesn’t mean that I dislike him, just that if you’re rating the one as an ace,you really need to look at the guy that’s better in the same light.
FWIW, I think of Bello (right now) as SP2 with the potential to be an SP1. Pretty much exactly of how I think of Luzardo too, for the record. I don't think anyone has called him (or Bello) and "ace" though. I think people have said "potential ace" which is certainly fair for both pitchers. Neither is there right now, however.
Personally, I think Bello is a bit more valuable than Luzardo right now, because you're talking about 5 years of control vs 3 for Luzardo. Though, for what it's worth, if I could give up literally any prospects in the system, in any number for another Brayan Bello, I'd do it. Luzardo, I'd probably hold the line at not dealing Anthony because of said injury history (but that is relative to the specific pitcher and not the concept). But don't get me wrong, if you could get George Kirby (more valuable than Bello, but closest comp I can think of) for Anthony, Teel, Mayer and Bleis I'd not only drive them to the airport but pay for their flights and snacks on the plane. Seattle would never do that, though.
But the overall point remains, short of a Jackson Holliday player (top 5 prospect, crushing high minors at a ridiculous spot on the Age Advancement Scale), I don't think the Sox - or anyone - would be able to trade "hitting prospects" for MLB starting pitching.
At least not on anything close to "equal" value.
*If the Sox (or anyone) wanted to offer something like Mayer for another team's version of Kutter Crawford, yes, of course they could do that. But I hope I'm making my belief clear enough about making a move for someone like Luzardo (or Bello).