It benefits some of them, but there are only a few teams that really blow past the luxury tax threshhold, so it really doesn't change a ton at the top end. But, combined with a floor, it forces the bottom third of teams to spend more money than they otherwise would have. A cap can be implemented in a way where the total of player salaries is comparable or even higher than it was in the pre-cap era, while also helping to establish a bit more competitive balance. MLB is never going to be the NFL in terms of payroll parity, but having some teams spending 3 or 4 times as much as others just doesn't make sense. The "other owners can do it too" argument doesn't work, because we already know they won't.