"Sharing" 90% of the hardware, well I'm not so sure about that. I mean if you're talking in Van Neumann machine terms then ok, theres a CPU, Memory, Secondary Storage, Output fine - but in detail? They're using custom SOCs, custom hardware for auxialliary tasks, custom SSDs, different RAM architecure and bandwidth....
But anyway, regardless of that from the software perspective they seem 180 degress opposed.
I mean the xsex is "a PC" - ok a customised hardware PC, but recognisable as a PC.
PS5 though - the approach they're taking to cpu capping for power rather than clock will make the optiomisation steps very different. On top of that, Sony want devs to be able to push data through the system at a rate where RAM could be reloaded in "real-time" without the need for a whole block of RAM set aside for scenarios that may not occur.
Then there's sound processing which Sony seem to have spent a lot of time on. New Dualsense - let's see what's in there.
To me, the PS5 is quite a big revolution in terms of software. There's a lot to chew on.
I don't feel "sharing 90% of the same hardware" is really doing justice to the differences of approach they've taken.