It’s worth pointing out that every MVNO negotiates a certain priority on the host network for its customers. This quality of service class (QCI) determines what peak performance customers can see depending on what type of traffic they are generating and how many other customers are competing for bandwidth on that tower within that specific network. A very simple rule of thumb is low QCI means higher priority. Emergency voice lines for example are 0.5. In the case of US Mobile, customers on Verizon (Warp) or AT&T (Dark Star) get QCI 9 (or 8 on the better plans), whereas their customers that opt for T-Mobile (Light Speed) are guaranteed QCI 7.
I used to be on T-Mobile’s network with US Mobile because that is the network I originally switched from. I didn’t notice any changes (QCI 7), but I also never liked that T-Mobile’s coverage could be a bit spotty at work. So I switched to using US Mobile’s Verizon network where I still am now. Noticed better coverage at work but no difference in areas where coverage on both was good. After a few months I switched to US-Mobile’s high-end plan and that took me from QCI 9 on Verizon to QCI 8. I honestly never noticed any difference at all even though here in Berkeley, especially when school is in or it’s commencement, the networks get very crowded, you see bars drop, and there’s certainly lots of prioritization going on. Heck, carriers even bring trailers to town to run auxiliary cell transmission sites from so their networks stay up at all.
Around here in everyday use I do see 5G UW a lot, but this is also in a very urban and highly populated area (and back when using T-Mobile on US Mobile it was a lot of 5G UC exploiting the mid band spectrum they acquired via Sprint merger). If you go out to the sticks (try Highway 6 in NV or around Uvalde TX), it stops showing up at all and at some point you’ll be happy to get just one or two bars of LTE. 