I have a MXIII (S812, Android 5) and a M8MiniII (S905X, Android 6), both will show simultaneous WIFI and Ethernet connections in Andriod if I turn WIFI on and connect.... I cant say I ever noticed and degradation in network speed though...
Thank You for sharing that info.
I seem to vaguely recall boxes i've owned in the past, which did this but never gave me any connection issues so i never worried about it.