That's not impressive, I reach almost 31,5MH/s with 2 of my RX 570s on Phoenix, and they are at least 50% than a 1070.
1080 with pill should be around 50MH/s. We've seen reports of this kind of pseed with ETH pill & Phoenix.
I don't think you earn more on ethminer rather than with Phoenix and its 0,65% devfee. You could buy a sub 15$ win 10 licence and compare.
I get 32.5 out of my 1070s and 37.1 out of my pilled up 8GB 1080s (averages.) I think those getting 50Mh/s are running 1080ti with 11GB.