I already said this, it's fulfilling a non-existent hole in the market. Yes there is a place for enthusiast class or higher end computational hardware but it needs to serve a necessitive function.
This isn't the same scenario that brought about the creation of the PlayStation 4 Pro and the Xbox One X. There was a legitimate need for a console that could produce 4K capable rendering for the transitory stage from 1080p to 4K TVs.
I can't think of or see a single reason or necessity for the creation of this, what void is it actually filling?
Introducing developers to AI-powered silicon solutions that can ease their development workload would be the obvious answer, especially for things related to auto-LOD generation or the such.
However, PSSR as it sounds, while very interesting, might only resolve part of that workload issue in practice as it deals with upscaling internal framebuffer resolutions. So in theory, developers only need to produce assets (mainly textures) at a level that'd work for a lower internal resolution that PSSR then scales up, so that would save dev time for artists on creating high-resolution textures, and could help with lowering game file sizes.
That said, it's only specifically targeting one aspect of the game development pipeline; stuff like PSSR can't do anything for auto-generating smart LOD models of higher or lower detail in real-time from source assets and metadata to program (or condition) silicon to know what to scale up/down and how, because that would be done with complementary technology in a future hardware design (maybe something like a PS6). And that type of technology could hopefully also sample the framebuffer to know what LOD levels would be needed based on calculated distance and position in the viewport (the player camera setting the viewspace for the framebuffer, basically).
There is already some amazing AI-based technology out there that can do things like generate 3D meshes of objects from simple photos.
Magic123 and technologies like it, are things Sony need to be incorporating into the SDKs and silicon of systems like the PS6, and expand upon them like being able to do the aforementioned things I was mentioning above. Pairing that with stuff like PSSR would be a boon in significantly speeding up dev times and lowering development costs.
So if PSSR is the first step towards that type of future hardware, then yes PS5 Pro does have an important purpose for devs in getting them used to developing games from the ground-up with specific internal resolutions in mind that can be upscaled very well from that to a higher resolution, meaning there are some things like texture assets they can ease up on in terms of file sizes and detail levels which will help at least speed up those parts of their game development.