You know ... it's funny -- I remember when it was en vogue to refer to T-Mobile as a clown company, even as they were assassinating AT&T and Verizon for their horrible behaviors. "Something something, T-mobile wouldn't have to do this if their network and coverage wasn't ass." "It's all just smoke and mirrors to get suckers to subscribe to their craptastic network." I remember forum members here arguing that they wanted carrier subsidies back - even though the carrier subsidy was -literally- smoke and mirrors for an instant loan that you unknowingly paid back though the base service fee you paid (and that you never got to stop repaying after the 'loan' was paid off). The best you could do to 'stop' repaying that instant loan was to buy a new phone. (but, that said mobile phones were evolving light speed at the time)
Now, no one can criticize T-mobile, in that same fashion, because as you point out they're now the number 2 carrier, having displaced AT&T. Because their network is not a joke and their subscribers are sticking around because they are generally well served. But, it's not lost on me that T-mobile has "lived long enough to be come the villain". That said, if T-mobile is now the "bad guy" while still gaining customers and while still kicking both AT&T and Verizon in the nuts -- Maybe AT&T and Verizon want to "un-carrier" T-Mobile? Because T-mobile -is- going to become the number one carrier.
AT&T is still gaining customers as well. It's only Verizon that T-Mobile is "kicking in the nuts." That's mostly due to Verizon's lack of 5G coverage (outside of metro areas) since they are behind T-Mobile and AT&T in that aspect as they lack the amount of low band spectrum T-Mobile and AT&T have, on top of them having the most expensive plan prices AND them requiring premium plans to access their "Ultra Wideband" 5G network while AT&T and T-Mobile allow 5G+ and 5G Ultra Capacity on any plan.