Im sure the timings differ and that could boost performance, but considering the Vega 64 can do 43mh/s maxed out, just tighter timings cant be pushing a 90% increase in peak performance, can they? (bear in mind these are stock timings, so they wouldn't be as aggressive as the STILT's straps).
Memory bus can be an additive factor, but then the GTX 1060 run a 192bit memory bus and outperform the 256bit RX 470/480/570/580 cards at same clocks (without bios mods ofcource).
Something tells me the Vega 56/64's are crapping out due to some other reason ...
I don't think 1060 wins vs AMD cards even at stock...some are even, but new ones with Hynix memory definitely
don't come close