Trademarks deliberately put the hand on the scales, creating a monopoly to the benefit of the entity that receives the trademark. Revoking the trademark takes the hand off the scales. That is pretty much the definition of a level playing field. Do you think that there's going to be another sports team called the Redskins that's going to come in and take business away from the current team? Get real. We're talking about T-shirt sales here. The unfairness that you propose is nonsense, because the other teams get no benefit from it.
You're probably too young to remember, but back when I was a kid you could get really awesome T-shirts sold by vendors who weren't licensed. And then at some point the teams and the bands realized that they could monetize their brands, and started selling these crappy-ass T-shirts that were nowhere near as good as the stuff the independent vendors sold. _That_ was when the thumb came down on the scales. That was when the playing field became no longer level. If the Redskins permanently lose their trademark, Redskins fans will once again be able to get awesome schwag, just like in the good old days. As far as I'm concerned, this is a win whether they continue using the name or stop using it.
That said, I think they ought to stop using it, because it's in insanely poor taste. If they just pick a new name, they will be able to trademark it immediately, and sell T-shirts with the same monopoly they had up until this recent PTO decision. They might see a temporary 10% blip downward in sales if they choose poorly, or they might see a sudden surge in sales if they choose well. But no matter how this comes out, it doesn't amount to a hill of beans. This is just not a big deal.