In Crash 4 that 10% difference is caused by difference of packaging methods. Traditionally PS4 games are a bit smaller than Xbox games because of this. Things will be very similar with the 10% additionnal compression given by Kraken (PS5) vs Zlib (Xbox).If consumers care about 10% less space due to larger file sizes, then Sony's in big trouble for having a 23% smaller drive to begin with.
In reality, almost no one cares.
But most importantly I think there will still be games on Xbox hamstrung by their PC roots. In Control only the PS5 (25GB) got the true next-gen packaging as it must be easier to make only one package for both PC and Xbox Series S-X (42GB).
So eventually PS5 could actually be able to store more games than Xbox Series X.