Maybe a little bit late, but:
I used my RT-AC87U until January 2020 for my 1000/50 Mbit line (also coax cable in Germany). Connected using gigabit LAN to the cable modem (DHCP), only using DHCP, DynDNS, port forwarding, Wi-Fi and guest Wi-Fi features of the AC87. Of course, my main PC and server...