MT with standard drivers (wifiwave2 drivers are not available for hAP ac2) uses too small A-MSDU and A-MPDU sizes to get those high net speeds. (The payload per transmission is too small).
Download is the MT transmitting, upload is the client transmitting ???
http://forum.mikrotik.com/t/ac2-vs-ac3-wifi-not-over-200mb/148289/1