@tential
You forgot that Tahiti performed very well when it was released. The 680 came after it, with the goal post known, despite that, it was barely faster (single digits, 5% IIRC) when it launched. OC v OC, the 7970 beat it. Back then when some of you thought OC wasn't an important factor! AMD got the lead with the Ghz ed and never looked back since.
R290 on release was close to 780 in performance. R290X was around 10% behind 780Ti. But here's the kicker, R290 was $100 cheaper and R290X was $200-$250 ($750 v $500?) cheaper.
Now the R290 routinely beats the 780 with a large gap, to a point where the 7970Ghz or R280X which used to be 20-25% behind the 780 is matching it. R290X routinely ties 780Ti or straight up beats it in modern titles. GCN has outgrown Kepler.
So your statement that we are ignoring gaming performance besides looking at the tail end of a GPU lifespan is false. At their prime, Tahiti and Hawaii were very competitive. This was reflected in the marketshare too, prior to Maxwell's release AMD was spiking up from 37%, I mean a 40:60 ratio is extremely good compared to where they are at now.
As to the current situation & moving forward, GCN will outgrow Maxwell for the following reason:
DX12 solves AMD's 2 biggest weakness which handicapped their performance in the DX10/11 era.
1. Driver overhead & single-threaded drivers. DX12 reduces overhead, has native multi-thread rendering.
2. GCN being designed for parallel execution of graphics & compute is unable to do so in a serial environment of DX10/11, really running crippled. It can run free with Async Compute usage in DX12.
Earlier in the year, I had made a comment that by this year's end, we'll see the R290 beating the 970 and R290X matching the 980. We're seeing that with recent games.
In the DX12 era, the R290 will match the 980 and the R290X will beat it. Obviously the refresh 390/X do a bit better.
When Artic Island & Pascal is here, we'll see how revolution the new architectures are, whether NV is all aboard the Async Compute train (more parallel engines). If not, then I still see GCN as being more future-proof, for such an old tech.