and the fact that Vega will have support and driver improvements for years to come. Whereas 1070/80 will likely get no more driver improvements.
Concerning the support that depends on how well Vega sells... Support for enhancements was/is subpar on Fury. Delayed wattman (it was still AMDs flagship at the time), no enhanced sync (will it come ? Probably), still no Async reprojection on anything but Polaris, that came out in april, Fury was still the flagship in theory, that's just off the top of my head, because those are 3 things that affect me directly and that wouldn't have happened with Nvidia (ok they don't have a wattdude equivalent)