With an external antenna aimed correctly I'm sure you'd get a much better cell signal. That may be what your neighbor has.

Keep in mind T-Mobile and AT&T are entirely different providers. AT&T coverage may be better where you live.

There are too many places that don't get 5G in the first place.

Yet unlike ground-based service in my experience, the situation is improving with time. It took 15 years for my old place to go from 2.4 Mb/300 kb to bidirectional Gb and that only happened because AT&T was feeling generous briefly in 2019 w/r to expanding service (in that case, 400' of fiber to my cluster of houses). They stopped expanding shortly thereafter because so many people were in exactly the same situation that they were swamped with requests.

I get around 48-56Mb down tethered to my 5G T-mobile phone. (in the north Seattle area)

Same latitude, lucky to get 2 Mb in either direction. But down in Roseburg, Oredgon I got 135 Mb/s download sitting in a parking lot so it's not my phone.

Edit: I just walked through the neighborhood repeatedly invoking speed test and I can get 50 megabits at various points. But I can't get it anywhere on my own property. There's no real rhyme or reason that I can see as to where it's good and to where it's bad.