Well since Sprint hasn't existed for 6 years now, they can't call themselves anything
While I get what you are saying from a historical perspective, is it even relevant? All three carriers use multiple bands. Verizon and AT&T have 1900 MHz, Sprint had 800 MHz that T-Mobile acquired and either offloaded or is looking to offload and I believe T-Mobile has some native band 5 in very limited areas.
AT&T is mainly AWS, PCS, WCS, DoD, C-Band
T-Mobile is mainly DD, AWS, PCS, BRS
Verizon is mainly AWS, PCS, CBRS, C-Band