I agree, the wow factor is nice but the graphics difference will be something for fanboys to wage war over. I also expect XGS to do a wonderful job of scaling the games up and down. Concerning gameplay, I imagine Sony having the edge since IN THEORY they can get to work on gameplay that takes the Ryzen Cores and SSD into account more aggressively compared to XGS. But this assumes that they is a new IP on the Horizon which I can't see. Who knows, maybe Horizon 2 will do some crazy stuff.
I don't know, just because devs have access to the zen cores, more ram, ssd etc does not automatically mean they will innovate gameplay beyond what this gen has done. I hope they do otherwise it will be a dispointing gen.
At this point it's impossible to make educated speculation how launch games will fair.