To be fair, vega 56 at launch was very competitive with the 1070 & 1080, particularly at launch day pricing. I bought my 56 for £389 which was similar money to a 1070 at the time and so far in my testing it easily outpaces stock clocked 64's and 1080's and is on par with a well clocked 1080. I won't deny that the chasm between the 1080/vega series out to 1080ti and titan is a little annoying but then the prices are IMO totally bonkers past that point anyway. I'm still a little baffled as to why the vega cards perform where they do considering the computational horsepower on board. My 56 will quite happily push nearly 1 million PPD whilst folding which puts it almost on par with a 1080 ti.
My previous card, a GTX 780 was the only nvidia card I've owned in nearly 25 years. Whilst I can't deny that it was a superb performer that lasted a decent length of time, it was frankly excessively priced, particularly once the 290 series came out. The 290 series hadn't been released when I bought the 780 in 2013, else I probably wouldn't have bought the 780. At least the 780 was a cut down titan unlike the current gen which are overpriced mid range silicon.
The one thing I did experience with the 780 during my time using it was the lack of being able to try out 3d in crysis 3 using a panasonic plasma as it wasn't a "3d vision" proprietary display. Yet my previous HD6950 was quite happy to do it albeit at poor framerates. PhysX was another annoyance as it looked great but you end up tied in to nv or experiencing abysmal framerates by using the cpu.
Lets just say that this GPP crap isn't likely to lure me back to team green. Too much in the way of anti-competitive behaviour, closed off feature support and proprietary features. Linus Torvalds had it right with what he said a few years ago.