From all I have seen Vega/RDNA1 has to do it hard way. Vega has good compute potential and if AMD manages some driver level magic for proper scheduling, it may not be worst. But I expect that RDNA2 will smash Vega in this like a bug. Especially in terms of completed operations per Watt-hour. (energy efficiency) As there RDNA2 should have much higher potential in similar TDP limit.