I think Sony had their tech nailed down earlier than Microsoft did. That's not too shocking to envisage.
To be fair, MS and AMD were pretty tied in with other over RDNA 2 specs and tech. Seeing now how much integration there is with MS tech such as VRS, Mesh Shaders, Direct RT, Direct ML, SFS etc, I have no doubt it took a little longer to get to the point where all that was finalized.
You can see how MS has been working hard to make Direct X the default API for PC.
MS has ingrained Direct X 12 U and it's new extensions into both AMD and Nvidias new cards.
I think the XSX was just as important to MS from an API point of view.
Looking at it now, with both AMD and Nvidia promoting the new DX12 extensions such as VRS, Mesh Shaders, SFS amoungst others, and these also being on the XSX/S, I can see how from a development point of view, this could be the default third party development environment.
Will be interesting to see if this proves correct or not.