It could do.
But then it might not either.
Think of it this way, the RX480 is getting close to the 1060 now with the latest driver releases, so lets call them even. That is the RX 480's 5.8TFlops vs the 1060's 4.3TFlops.
So that is about a 34% TFlop advantage to the RX480 and yet it just about breaks even.
Two RX480 fall somewhat short of a 1080 let alone the TitanX
Vega's supposed 12TFlops is about 10% more than TitanX's 10.9Tflops.
So Vega would need to find that extra from somewhere, maybe all the optimising AMD has done, the reworking of the core might very well do wonders for its pipeline efficiency, who knows.
We will just have to wait and see.