Once PS4 is properly ditched engines will push PS5 back towards 30fps in some instances. So PS5 Pro will be about hitting natvie 4K, 60fps/120fps (latter is a little more niche because of display tech also needing to support it) and Ray Tracing. I’d say RT has the potential to be the differentiator if a substantial tech improvement in that area is made - rather than the sellotape two PS4’s GPUs together approach of PS4 Pro (despite that being quite clever).
The Pro update is always going to be a small step change though, and it’s targeted at those who want some extra shininess, framerate or resolution.
In terms of cross-gen currently there were good reasons to continue support (shortages, increase game dev costs) but I still think PS5 offered enough of a gap outside of general prettiness to be well worth entry price so far. In particular loading speed change and framerate/graphic options.