C-band is further from becoming a reality than CBRS is right now considering there still hasn't been a decision made about if satellite operators should be able to sell it or if it should be auctioned off. And even then, it'll probably cost an arm and a leg to acquire. CBRS is shared spectrum that will likely be split up into a ton of chunks which doesn't exactly make it pristine mid-band spectrum.
Sprint's advantage is that 2.5GHz not only has better propagation characteristics, but that the whole 120MHz+ is available to them virtually nationwide. The main advantage of CBRS is that it will likely be the first "global" 5G band and will be useful for roaming purposes. For that reason, I could see Sprint along with every other carrier and cable co trying to get some of it.
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.