I think PS5 and Nextbox will continue to be very close to eachother in graphics, and the slight edge that one have over the other wont matter for sales at all.
Most people think PlayStation is the place to play videogames, and most people don't even see any difference in graphics between PS and Xbox. So PlayStation will sell more, since it's the mainstream choice. The only thing Sony has to do to stay on top is up the graphics, have the same controller and do the same kind of games. They have it very easy compared to Microsoft and Nintendo who has to innovate.
I only see MS winning if they introduce their "netflix of gaming" version and are successful.