Eventually service will improve. Presently Sprint and T-Mobile both dedicate spectrum to the same thing. They have to reserve some spectrum for legacy applications while optimizing for newer technologies. By combining their spectrum they might be able to reduce the aggregate spectrum necessary for legacy applications and better utilize spectrum fro newer technologies.
It might help with coverage as they aren’t needing 2x as many towers to cover the same area, thus potentially justifying adding towers in new places, but I wouldn’t hold my breath on that happening in any broad way.
