Depends on the speeds you were getting, and how many other devices you have on the network, and whether you have wifi channel contention or not.
If your Xfinity was constrained (weird) but TMobile was not then you may haver reached the pinnacle of throughput already.
I use a wired connection for my day job, and T-Mobile as a backup. My router switches between them as necessary. I have to say I’ve not had a problem with T-mobile, and my music doesn’t sound magically better when I am on or off it, but when my landline goes down, of course, it sounds terrible. :D
Honestly though, unless your streaming service was severely speed limited, which could happen for a variety of reasons, including routing, I’d expect most streamers to easily handle a variety of upstream situations thanks to buffering. If your streamer is "sensitive" to cable providers, it may be worthwhile getting a new streamer.
A better "tell" for this kind of problem is video streaming. It takes more bandwidth and more clearly visible (literally) when it's slow. Compare how long it takes your video to start streaming at high resolution with each provider.