I don't buy that argument completely, nothing would be stoping them from just not bundling the drivers with Steam and also not requiring that I launch games through steam (if that is true).

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)