Pascal simply beats it because it's simply just faster. Taking 980SLI performance into one card would be faster than a 980ti or FX any day of the week. So it's not that the FX is crap, it's simply not enough horsepower to be in the same category. In addition to that, FX gains huge when using DX12, but still, it's simply to much power it's competing against. Solo cards is another story where the fX is fighting off every card that was in the previous generation. A 1070 would be it's closest competitor, but even then it's still simply more powerful it is basically a TX.
Also to point out. I think you are riding the Fury line too quickly. It's still very fast for today's games and as more games move to dx12 and people hold onto those card's, they just stay more relevant for longer
I don't any person bought a Fury X for the hopes of DX12. If they did, that's all on them. You never buy a GPU because of an API. I bought a Fury X yes, but my intent was getting the most I couldfor my money, and I did. Dx12 was the icing on the cake for me as I think it was for most people