I go back to the earnings call earlier in July when Su (I think it was Su), reiterated that the design focus for RTG had been shifted towards enterprise more and more and on this front, AMD is very, very competitive with performance and even more so with price. From the purported focus of what GCN/Vega is supposed to be in relation to AMD's market goals, it can be fairly argued that Vega is a success.
The problem with AMD here really is about marketing. AMD should have just toned down the marketing for Vega as it relates to gamers, rather than make nonsense ads like "Poor Volta." That was clearly very stupid...unless they were specifically referring to Volta in the enterprise space (which could only be a price/performance issue, imo)...but that wasn't really an enterprise-directed ad. It looked like it was aimed at gamers, to me anyway. That being said, it's not that RX Vega is bad in a vacuum, it's just that AMD is not competing in a vacuum. This would have been a decent release a year ago (still getting crushed with efficiency, though), but it is just very late to be meagerly competing with a mid/high-end card like 1080.
I agree that RX 56 should have been the gaming card, and save the full dies for enterprise where margins would have been much better....but I suppose there is a segment need where AMD wants to claim that it can offer options in the higher end. It just looks like a very poor effort to me. Obviously these are great cards/options for the many numbers of people that don't have something in this performance range (I will be getting an AIB 56 some time in September-November...I guess), but it appears very, very late and a bit too short. Vega seems like more of an enterprise design on the high-end/margin side of the offering, and a low-end-mid APU offering on the HPC/console space. I fully expect Raven Ridge chips to monsters within their class, so it very well could be that the actual design and market goals for Vega are very different than what consumers expected (and to no small fault of AMD's own marketing campaigns, obviously)