I read this on a YouTube channel's report on the new Doom benchmark run:
"Not only is the card 10 percent faster than the GTX 1080, but Vega is running without its proper graphics drivers, instead relying on the fury drivers to power it, and with a debugger layer slowing things doom even further."
With drivers, further clock speed increases, and without this debugging layer (I don't know what this is or its point), Vega could be more powerful than a 1080 in the same way the Fury was slightly more powerful than the 980.