I thank you for your concern. Some hardware was purchased, some was given... Hardware already out of return period... It would be advice for someone who's looking to buy hardware, not trim down like in my case, or adjust settings as in @AlphaGator1 's case. In the latter's case it would be good to try to optimize the settings, before deciding whether or not to return the BE19000Ai (which I am assuming may still be in return window)...Both of you guys @AlphaGator1 and @jzchen have to approach your communications (and perhaps surveillance) infrastructure the same way you approach your other essential electrical, water, drain, gas, fire, HVAC, etc. infrastructure - you call a professional and solve the problem once. The fact no license is required doesn't mean DIY is way to go. It is a waste of money on hardware doing something, somehow.
The 14x mixed make and generation APs in @jzchen house - no comment, SNB Forums Guinness Records application. The 6x APs in @AlphaGator1 house - the existing APs were too many already, but at least were capable of dedicated wireless backhaul. Added $900 AI messed them up with wrong radios configuration, it has features incompatible with the rest of the network and single 6GHz short range localized radio.
If you don't want advice - cool.
There's a significant difference (now) between low power mode and standard power mode. Standard power on one router appears to illicit reciprocity in other WiFi 7 routers, as I experienced 6 GHz backhaul between Ai router and BE98 Pro from South end 1st floor to North end 2nd floor. There was no problem with 6 GHz backhaul between GT-AXE16000 and GT-AXE11000 way back in 2022 when there was a floor in between them (both South end rooms)....
I've noted that TP-Link Range Extender specs show < 30 dBm across all 2.4, 5, and 6 GHz. You've referenced material that that is no longer the case. So OLD firmware I suspect should return such routers as the GT-AXE16000 and GT-AXE11000 back to higher power 6 GHz broadcasts, I suspect....