Valve’s repair policy was exceptional with the steam deck so I have reasons to believe that the battery for the steam controller will be available for a very reasonable cost.
Just to piggy back on what you are say, one of the engineers in the LTT video mentioned they want to team up with iFixIt again, just like they did for the Steam Deck. And I saw the back shell off the controller in one of the videos. The batter looks dead simple to replace. It's wild to even imagine that a company in 2025 would be be consumer friendly.
If what you want is Windows. Just use windows. For the few times I've had to use Windows over the decades, while frustrating and laborious, I don't expect it to be like my Linux distro. If a Linux distro has the features, utility, software, or ease of use you want. Then by all means, buy a Linux compatible machine. Most distro's install in 5-10 minutes or buy a prebuilt Linux machine. Nobody expects MacOS to be Windows or Windows to be MacOS. And why would you? Just use the OS you need. Imagine expecting MacOS to be a "free Windows clone". I'm sure the MacOS users would be screaming bloody murder if Apple thought that was a good idea.