My sister in law has AT&T, and her boyfriend has T-Mobile. So we are a full spectrum of the American cellular network. We all get full bars of "signal" while outside, but Verizon is the only one (4g or 5g) that will actually connect to the internet to do a speedtest.
Everyone in town just chalks it up to that is the way it goes, but worse than that, we only have one internet provider in our area, and from Christmas to New Year, we had a total of 50 hours without internet.
We live in a tiny tourist town that is a 45 minute express train ride to/from NYC, and while we may be close in travel, we are very distant in our available amenities.
T-Mobile has also been doing a big rural buildout, and even built a map to show coverage on all major carriers: https://www.t-mobile.com/coverage/lte-comparison-map