Sony has put alot of effort and resources into their dev tools.
They are the best in the buisness.
I think there were a couple of reasons Sony stuck with the 36CU GPU, one being to make BC easier, and the other was to make the changeover from PS4 development to PS5 as easy and familiar as possible. Thats my thoughts, not claiming Sony said this.
Sony was also well ahead of MS with releasing dev kits to studios, and this would have given devs a quicker turn around for their PS5 development.
MS on the other hand totally changed their GPU, and added a number of extra API extensions, all while being behind Sony with releasing dev kits into the wild.
Its pretty reasonable to assume that this would have given developers a leg up with their PS5 games coding over the XSX. And again, it's pretty reasonable to assume this would result in PS5 versions of games being better optimised than XSX ones.