I don't think a $600,000 player making $2 million is as big a problem as teams carrying $70 million payrolls when it should be twice that. Those players should all already be making $2 million now. But it's up to the teams to distribute the money correctly. And if there aren't enough good players to support that, don't expand. But the money is already being made (leaguewide). And the good players are already being paid, they just wouldn't get traded by lower-budget teams if a salary floor equalized the budgets across the league. Teams like the Rays would keep their stars and spread the money out across the bottom of the roster, while a few teams would give out stupid contracts to get there. No different than now.
This is not generallly a problem in the other leagues. Nobody is overpaid on the Sixers because there is a salary floor. The top rookies are getting $1-5-$3 million but that's also all the veteran free agents get (at the high end).
It is the least of the problems with the concept, the revenue-sharing piece is the bigger obstacle. For all their admirable baseball savvy, there are just too many teams that can't actually afford to field a competitive roster, and then claim they need public funding on top of that. And yet somehow the richest teams want it too.