Buying through T-Mobile may be a more intuitive way of getting one's hands on a OnePlus 7 Pro in the US. However, those units of this flagship are often subject to restrictions that keep them on this carrier's software update plan for a set amount of time. Now however, there is a possible solution to this situation.
https://www.notebookcheck.net/OnePlus-7-Pro-users-on-T-Mobile-can-now-convert-their-phones-to-international-units-without-the-usual-hurdles.422926.0.html