The more sub 6GHz spectrum the other carriers pick up, the less advantage Sprint has. That advantage holds a bit tighter though for anything above 2.5GHz for realistic urban full on coverage.
However, it's a long ways to get there. CBRS is 150MHz right now, that will get split up once it goes up for auction. And it's a full 1GHz spread from 2.5GHz.
Then C-Band that is being looked into like 6GHz, you are looking at similar limitations that are on existing 5GHz. Unlicensed, low power output of 1w or 250mW. With current considerations there will be at least 850MHz for 1w output, but that is still just 1w.