TBH,my GTX660 was cheaper than most HD7850 cards and my GTX960 4GB was closer to £100,but if I paid more than an HD7870 for my GTX660 or more than an R9 380 for my GTX960,I am not sure whether it would have been the wise choice longterm IMHO OFC.
The whole point is that the top end Nvidia cards still have enough grunt but the rest of the product stack below the GTX780 is not as high performance,so is suffering in comparison.
Edit!!
But this is part of the problem for AMD. I know plenty of HD7850/HD7870/HD7950 users who have not bothered upgrading since their cards still are doing well.
However,OTH I know more people like me with the equivalent Nvidia cards having upgraded sooner rather than later.
In some ways,AMD has shot themselves in the foot.