If we have learned anything in recent times, it's that we should never count AMD out.
Intel stagnated for years with the core architecture, giving tiny performance bumps, having a tonne of artificially hobbled SKUs, and blocking upgrade paths by changing their underlying platform year after year. All of this without even the smallest indication of trickling HEDT technology to mainstream.
In servers they had (... or still have, tbh) a complete monopoly and were charging whatever they wanted for high core count parts. (although this is also to do with their monolithic manufacturing process...).
Laptops and mobile, AMD's parts just did not compare. Sure AMD had some interesting APU parts over the years but they weren't appealing enough to get into any mass produced, high end devices.
Intel left the entire PC market to stagnate as there was simply no reason for anyone who had a second generation(or newer) quad to change to upgrade. They left the door wide open for AMD, who did an incredible job in creating a profitable and scalable platform to get back into contention for just about every market.
Although it's easy to make the comparison, I don't however, see the GPU market being the same as the CPU one.
Nvidia and AMD, over the years between the 4*** series to the R9 3** series were pretty equal with Nvidia; trading price/performance/watts metrics from generation to generation, but they haven't seen a relative hold on the market to represent that. People buy Nvidia because, "it's the way it's meant to be played".
We're now in a situation where Nvidia doesn't have to release their parts into the mainstream at all, but due to AI and the various sub-markets that relate to it, they are still being pushed to develop them.
Look at Volta. They claim that it was never designed for consumer products which is why it only ended up in an uber expensive titan or quaddro sku, but you better believe it would have found its way into them if there was any competition...
We still dont really know what Turing is going to bring to the table, I suspect we never will know what Turing COULD bring to the table, as Nvidia has nothing pushing them to drive their higher end parts down the market segments. They will do just enough to make people buy them, but not enough to really shake things up.
I think we all thought intel had parts sat waiting to drop on AMD to keep control of the market, so we were a bit surprised when the best intel could do wasn't all that impressive. With Nvidia though, they haven't left the door open, there isnt really anyway for AMD to slide in without a swift Nvidia response that I can see.
If Navi really is just a 580 replacement, then I suspect the mainstream GPU market will continue as it is, with Nvidia dominating the high end and AMD doing an OK job at providing a good value option for the larger middle section of the market.
If I was to offer a suggestion about what they should do, it would be to target the frustration that gamers have with Nvidias 20XX series, and that is the lack of focus towards CURRENT games in 4K. If they can get a part out that pushes the framerate of current titles with current technology beyond what Turing can deliver @4K, they could undermine Nvidia somewhat. I just don't know how they could do that... but like I said, don't count them out.