Let's be honest about what AMD are claiming though, they are only claiming 4k 60FPS performance. How it compares to 1080 or 1080ti performance is only applicable when comparing prices, which from AMD will likely be a little under the comparable performance from Nvidia. This is the most likely reality of Vega, whatever performance they come in at, it'll be priced a bit lower than Nvidia. I don't expect more than that. Whether that equates to a massive fail for AMD I couldn't care less about, as that's mostly a subjective viewpoint. What counts is bang for buck, and AMD have a market there, whether people want to admit it or not. Doesn't matter if it's 1 or 2 years late, they are never going to "steal market share" from Nvidia, despite any aggressive marketing ("Poor Volta").
I'm tailoring my expectations for a faster card than anything AMD currently have, competitively priced. No way are they ever going to have the fastest card on the market, nor do they need to. Yes, it would be a huge gain for AMD if they did, but only the most optimistic of people would hold out hope for that.