OK, let's go:
Will Spyderman MM and Horizon FW be retained with PS4 versions?
Of course yes.
The Jaguar CPU on PS4, and literally the biggest problem here. Maybe someone has already noticed, but 2 cores of the PS5 CPU yield more than all 8 cores of the PS4, not to mention the extra earnings from the architecture.
So what are we getting?
PS4 assets..
Well the fact is, a PS4 version has to work on PS4. So you simply cannot cut the CPU, geometry and design have to be the same in both versions or they are not the same game, so starting from that is already a problem:
Insominiac (and no details have yet been given) using 1080p30fps PS4 as the base version of Spyderman (MM) 4k60fps is more than mandatory in the PS5 version as we are seeing a difference of almost 10 times of raw power. (Not counting the optimizations architecture).
Even the poor SSD is underutilized here as the game has to run on the HD 5400rpm. Literally begins PS5 with 4 flat tires.
And if Halo's criticism was about an Xbox One version delaying the new generation, here Sony stuck in the puddle ...
Horizon FW apparently will suffer literally double, while Insominiac has two titles and the Guerrilla has focused on this game since 2018 (this would be Sony's Halo) the most important game on PS5, downgraded to crossgen ... the scale of the map, drawing distance, the game's own mechanics and interaction with the world, geometry and of course RAM will literally be for other games ...
Taking advantage of God of War Ragnarok will have a PS4 version?
I don't think so, because they didn't say anything about Rachet and Clank so it's 80% exclusive to PS5 (but of course if you told me Horizon FW has a PS4 version, I would also doubt it and accuse you of FUD) .