The big shift came with Maxwell I think. If you sort the results by
Bedroom scores (the tougher of the two tests, stressing incoherent rays), on page 2 currently, you'll see that kklors' massively powerful 8-core Haswell-E at 4.6 GHz gets a slightly lower score than a firstgen Maxwell GTX 750 Ti (!!). I bet it wasn't even overclocked, those little GPUs have a ton of headroom available...
Anyway, it seems impressive to me that the little GPU is kicking so much ass compared to the previous generations from NVidia (and high end CPU-based systems), where AMD were very competitive with eg the 7970. I think it has a lot to do with the 2MB L2 cache and reduction of dynamic thread scheduling logic. Pascal added a large generational improvement on top (finally not 28nm, 2 GHz core, 8 GB memory), so it's in some way not surprising that they are winning right now.