That article has another ridiculous quote by Karl in it.
The issue is not that there isn't enough spectrum- there is. The issue is that it is horribly divided, cut up into a ton of tiny chunks that are whackily distributed through a long history of M&A, instead of being leased by the government in the first place.
If you accept the status quo of ownership, then T-Mobile should have actual ownership of their spectrum, and with that ownership, the right to sell it to whoever they want.
AT&T is the shortest on spectrum relative to number of customers of any carrier. Verizon managed to nab plenty of spectrum through the 700mhz auctions, as well as from SpectrumCo, and likely they will buy SpectrumCo's 700mhz at some point as well. The T-Mobile spectrum, while not as clean as Verizon's purchase of greenfield low-band, would have at least helped them immensely, partly through the spectrum synergy, but also by acquiring more cell sites, which would have provided more density and more efficient use of the current spectrum. But no, the FCC doesn't like efficient use of spectrum apparently.