Source: Work in phone repair. We don't repair phones that cost 100USD new and have a non-existant parts market.
The biggest difference is their coverage. If you live in, and mostly travel within a metro area you're fine with sprint/tmobile, but anybody who's ever travelled will find that verizon is the only option if you work in, or go to the middle of nowhere at all. Basically Verizon has towers everywhere, including farmland that I can't figure out why they'd want to cover, but hey you get coverage while picking blueberries!
(This only goes for the USA, and includes my experience living in Michigan working in phone repair/retail, as well as my travels with other people/their carriers outside of Michigan)
I don't think Verizon can be considered high end, at least not definitively. Wherever T-Mobile does have coverage, their speeds are higher, and their offering of international roaming and by-default unlimited data are clearly geared to the "upper" end of the market of professionals that live in cities, that travel frequently.
EDIT: I admit I was initially skeptical about the claims being made against Huawei and ZTE, but as more evidence arrives, I (personally) think caution is warranted. Critical infrastructure is a thing. Offer trade in/replacement rebates if you want to reduce friction during the device purge.
Do you really want, hypothetically, a phone maker, say Apple, to get into a sweetheart deal with AT&T and make phone service on non Apple IMEIs unreliable? Or for AT&T to target certain political, religious groups ....
So no, they can't just do whatever the hell they want.
With that said, They SHOULD have a surcharge for ZTE phones, if they are hostile to their network.