I agree that RX570/580 is very good on the LBRY when dual mining with ETH, but for me its not worth it.  Too much electricity, too much problems if you have 6+ GPUs and your electrical system is not scaled for this.
dual mine vs electricity usage Works much more efficient on nvidias. But thats my opinion. That is why I dont dual mine on my ATIs, only on my Nvidia.

example:  RX570 - single mine ether, 125Watts,  dual mine ether+lbry  goes to 180-185watts.
Nvidia 1060 stuck at 85-90 watts (with lower TDP but still efficient mining hashrate).  dual mine eth+lbry.