They are believable, this is built with the same idea PS4 Pro was.
Minimal effort to get 100% BC with base PS5 titles, a little bit more RAM freed to devs by adding a separate/increasing the size of an OS specific RAM pool, a modest clockspeed bump to the same CPU cores (helps with the BC point above), moderate bandwidth adjustment of the main GDDR6 memory pool not to completely starve the GPU, and a GPU that has a mix of the next generation and the next-next generation cores with something custom by Sony peppered in. I would hope for a small NPU / AI cores though for devs to start playing with things. Not sure who has been screaming for 2x Tempest Engine performance…
This might be why these specs are true or false… because they look exactly how a PS4 Pro designer would design PS5 Pro (same architecture team yes, but having not changed their mind on any single detail).
This is not a console design where devs would get massive boosts just by brute forcing their way through which IMHO will lead to few devs really taking advantage of what it has to offer (aside from a few of them, likely first party, depending on how much of a preview of possible PS6 features PS5 Pro could be maybe). So, dynamic 4K at 30 FPS becoming 4K@60 FPS… doubtful

… we shall see.
These are the kind of specs I expected, if true, and reasons why I would have preferred Sony not to waste their time designing and selling it and launching a better PS6 a year or so earlier at least…