I don' think it's that simple. The commissioner and his owners want a cap, but they've done nothing to indicate that they want a floor - at least not one that would have any meaningful impact. The closest thing I can find to their thoughts on a floor is the pathetic $100MM they offered in the last round of CBA negotiations. Why would the MLBPA even consider an offer that chops hundreds of millions off the top end of team payrolls while only requiring a handful of teams to spend a fraction more? That's not competitive balance; that's salary suppression. I'm not interested in more of my money spent being a fan going to owners and less going to players.
I know increased revenue sharing goes hand in hand with any kind of arrangement proposed by the owners (and it should), but they have proven through the actions of some owners - as well as the tolerance of those actions by the others - that they are fine with it being pocketed by the Nuttings and Fishers of the world instead of being reinvested into payroll. Why on earth would the MLBPA not fight against this tooth and nail? It would be malpractice if they didn't.
A salary cap could bring the competitive balance that everyone wants. The other leagues are proof that if set up properly, then all stakeholders - owners, players, broadcast networks, fans - can benefit. The rich teams of those leagues that seemingly have the most to lose in those arrangements have seen their franchise values increase exponentially as the rising tide has lifted all boats. But that requires two things the owners have thus far shown no willingness to do:
1. Install a high floor in the 75-90% range that the other leagues have
2. Transparency in determining the revenue figures used to peg the levels of caps and floors. That means opening the books to the MLBPA as well as third-party analysts to not just identify the revenue, but proper adjustments for things like team-owned networks, team-controlled revenue generated around the park, etc. The NBA, for example, calls it "basketball-related income." It took a lot of pain to work it out, but the league has flourished ever since.
If the owners are willing to do these things and the players still fight against the cap, or fight against the revenue sharing that would make this work, then by all means, vilify the MLBPA as they would fully deserve it. But until then, the owners can take their cap and shove it