the ap it’s like a “magnet” for all clients on 3 floors who see the signal.
Analyze the beacons and you might find why this is. (e.g. BSS load info missing…
And as you look at beacons anyway, see A-MPDU and A-MSDU size what explains performance difference. http://forum.mikrotik.com/t/ac2-vs-ac3-wifi-not-over-200mb/148289/1
(Beacons on wifiwave2 to be analyzed, when hAP ac3 arrives one day)
MT is strict and correct in following the EIRP max power as per regulated region. Other brands easily go 10dBm higher, and in the illegal range. (Or are set as such by SW config.)