This is a windows issue, not a hardware issue.
While we could argue about the state of Windows, Steam also did not have to engineer it this way and the requirement of launching through Steam feels deliberate.
From what I can find, as others have mentioned, the 8BitDo controllers don't require Steam to be running to work. I presume the PS5 controller likely also does not (I will test this later)
My PC may have installed something on its own, but I did not.
However I don't have an issue if there is a driver, the requirement of Steam running and apparently launching the game through steam is the issue here.
Edit:
I just realized I completely missed the not in your message:
> I can confirm that you do not need a Sony/8BitDo user account or any of their software running in the background for the controller to work.
so I guess my reply was not necessary, I need more coffee...
"I refuse to accept reality, you are wrong."
You don't have to launch games through steam and the controller works fine, just like a normal controller. However if you want to take full advantage of all of the controller's features and be able to remap buttons easily then you can use Steam Input which tries to unify the awful mess that is input device standards across platforms and games.
If you don't want to then there are other options to take full advantage of the features like sc-controller. However this is not as user friendly as using Steam Input.
It's generally a good idea to read and understand before freaking out and getting outraged and spreading FUD.
Valve does deserve criticism for the royal pain certain things are though. For example non-technical users will absolutely struggle to get Proton working without Steam, the process in doing so is purposefully kept undocumented and esoteric. There's 100% a little bit of undesirable obfuscation Valve does to push you towards just using Steam to run their OSS. It's definitely non-Free in the purist sense.