Would love if Playstation still used, albeit performance being improved of course, the XMB (XrossMediaBar) from the PSX, PSP and PS3, that was the best, most organized, OS I've seen.

The PS4 and PS5 OS still uses it as a base, but it's not the same, you still have to go out of your way to access some other menus/pages, while the + format from the XMB allowed every major group to be easily choosen from left to right, and from there you pick what you want going up and down.

So yes, I have no problem with it and actually hope an old one would come back.

One of the few things I prefer about PS5's OS is that it is on an SSD so it's faster. That is when it doesn't freeze on me which seems as often if not more than PS4's OS.

I would've preferred Sony reuse PS4's OS. 

Not really. I suspect you're talking about the welcome thing, which seems like it can be customized a lot, but my issue is mostly with everything else, which seems like it can't be customized almost at all. Stuff's just scattered in all directions, and many directions require a different method to access. Settings and trophies? Up there, behind some specific button, I think? Options or triangle button, I cannot recall. Notifications and shutting down the console? At the bottom of the screen, accessed by pressing the PS button, except I think it's a long press. One day I'll learn whether it's a regular press or a long press, but that day is not today, because it's not intuitive. Sorting trophies? There's a separate button to the left, accessed by pressing left. Options button, as it was on PS4? I don't remember, but I don't think it was anything useful. The welcome thing also feels like something Sony didn't know how to design properly, so they just squeezed everything in there and made it customizable. It feels like everything there could be useful, but at the same time nothing feels. (Also, I'm pretty sure the contoller battery charge display there blatantly lied to me on my second time playing, or the controller battery is just terrible.)

On PS4, it's all simple. Two rows of stuff, which you can open for further inspection by pressing X, which depending on the selection might open a regular vertical menu. Press options for options, if there are any. For controlling power etc. and in-game stuff, hold PS button. That's it. There's a few small gotchas, but it always feels natural enough.

Welp, as much as like some of the kwirks of previous OS systems on Nintendo consoles/handhelds, I really can't disagree with the responsiveness and straight to the facts operating system of the Switch family so far.

From PS4 to PS5 the long and short PS button pushes have flip flopped.

https://www.playstation.com/en-us/support/games/customize-ps5-control-center/

This is all I customized and full disclosure I do not fire the PS5 up often these days.  My Switch and now Switch 2 got most of my gaming time.

Hmm, interesting. That's a customization feature I hadn't encountered yet, despite looking around quite a bit. Doesn't really help with the core issue where everything kind of scattered around, but perhaps I might want to customize my control center anyway. Regardless, this to me is a clear case where reinventing the OS was for the worse and I would much have preferred the old OS.

I can't think of anything that matters less than whether a console reuses an OS.