> without any kind traffic shenanigans, it's not a net neutrality issue?
Yep.
But they do rate-limit people: https://www.t-mobile.com/support/plans-features/activate-hd-...
If you're on the top plan then you haven't experienced it. The irony is that T-Mobile was one of the ISPs throwing support behind net-neutrality, and now they are one of the most aggressive net discriminators.