I dont think its that easy. Nvidia is at least one generation ahead and it looks like it will stay that way. Sure AMD can create a midrange chip, at the size of a highend chip, that competes with Nvidias 60s, 70s and 80s lineup in terms of performance...but their effeciency does not look so great atm. And while energy effeciency isn´t everything, if the disparity is as big as it looks to be right now, it will factor into reviews and the image those chips have in the public.
Vega should be their Titan-esque halo chip, but it looks like it will be around the 1080´s levels of performance, maybe a bit more but at a much higher die size, with exotic and expensive memory and a high power draw. Maaaaybe they will gain a lot once games optimize for it, but ~1080-levels of performance in the vast majority of games with a few outlier highend games is not that attractive.
Part of what made Zen possible was that Bulldozer sucked so hard, that they made a clean break more or less. GCN is still doing okayish compared to what happened with Bulldozer back in the day, so they are not forced to go back to the drawing board. They probably can´t afford it, too.