When migrating to a new router I remarked my iPhone (7Plus) had lousy TX performance compared to the other 80211.ac Apple devices connected to the same wireless SSID as revealed in below screenshot:
Since it was a new router, I figured maybe there was some inconsistent configuration going on somewhere. Reviewed everything; all good.
Comparative analysis: what's different about this iPhone than the other devices that are working correctly?!?!?
I remarked my iPhone was right next to the router. So I moved it about 4 feet away (in same room). Still terrible TX performance on just this one device. Other than proximity (which I just checked) which can affect wireless performance, why was this iPhone non-performant?!?!?