Yes, currently vega64 is not the most profitable choice for mining when you pay almost $700 for a card. However, there is some promise here when the price comes down and the drivers mature. I needed a new gaming card so I got one to test for mining too and I'm getting 41MH/s on ETH.
FYI, it auto throttles a little around 66C and a lot at 70C. My current settings are GPU S6=1577, ram 1025, target temp 65, power max -5%. Using the latest blockchain driver.