mmWave and Midband are two very different things. I think you might be conflating the marketing terms used (Verizon - Ultra Wideband, T-Mobile - Ultra Capacity)... with the underlying technology.
There are 3 general "types" of 5G
Low Band - Slowest but with furthest reach
Mid Band - Fast with medium reach (this is the one t-mobile is heavily invested in and verizon has also started rolling out)
High Band - Otherwise known as millimeter wave because it is the very very high frequency range. Meaning it can be wicked fast, but has limited range and is easily blocked by the flimsiest of obstructions. This is the one where Verizon has the biggest footprint among the carriers, but still tiny compared to coverage overall. You'll see this tech clustered at venues and the core downtown areas of big cities.
Collectively all the carriers refer to Mid & Band AND mmWave (high band) 5G as:
- 5G+ - AT&Ts designation for mid band and mmWave
- 5GUC - T-Mobile's designation for mid band and mmWave
- 5GUW - Verizon's designation for midband and mmWave