Doesn't matter that PS5 will progress. A ceiling will be hit. The Series X's ceiling is much, much higher. What do you think happens when they get Machine Learning upscaling working? The GPU for the Series X is designed to perform at its best best with Sampler Feedback Streaming. Literally no game is currently using it. There are very basic improvements that will come on the development side that will fix relatively minor seeming things, but will make all the difference in the world as far as making things easier on the developer's end.
That's where these strange, unexplainable performance related things are coming from where they shouldn't exist based on the specifications. Cases where the PS5 is outperforming Series X are examples of PS5 simply getting by on the bare minimum of optimization from a more mature dev environment. Once the Series X reaches that stage where certain things are no longer even a concern for developers, there will be regular, consistent and clear separation between these two consoles, and that's even before all the major headline RDNA2 features come into play. Microsoft waited for longer to finalize their hardware. There are major long term benefits of that, but short term headaches.