What I've noticed, and Sony confirmed in their video with Mark Cerny, is that everyone (75%) of people are playing on performance mode, because in Fidelity mode, none of the games are capable of holding 60fps.
The Pro supposedly provides Fidelity mode graphics (or near to) at 60fps.
It's really noticeable too, you either lose the nice visual definition with low dynamic scaling resolutions, and RT, by playing in Performance, or you get horrible frame rates and lots of input lag in Fidelity, but you get RT and nicer visuals.
If I gamed a lot (I don't much at since I have young kids, due to time constraints), and the price was a bit lower, I'd totally get one, but it's not for me, right now.
So I do understand who it's for; put that price tag stings a little.
EDIT: One big annoyance is that if you have a day-1 PS5 like I do, you likely wouldn't have bought the slim version, and if you want a disc drive, you'll have to buy that separate; There's not many people likely to have bought a slim with a drive to have it to swap onto the Pro, in my mind.
I can tell the difference if I'm looking for it on PS5/65"TV but I tend to set it to fidelity for the first session for that "wow" factor on a new game, then I switch to performance.
If I'm into a game, I'm only really going to notice in the cutscenes anyway after I've played for a bit. It looks pretty good anyway, and I'd be much more annoyed by high input lag and low frame rates/stuttering than slightly lower visual fidelity.
£700 in the U.K. is crazy