The point is that a PC has a million possible configurations that can affect performance. A pared-down environment, like gamescope, cuts down on most of the software-side issues that a PC deals with.

Yes, just installing a game on Windows and running it is pretty simple, but these days lots of games have anti-cheats which can be triggered by other software running (or even just installed) on the computer. Windows on its own has a ton of overhead due to all the background and telemetry processes always running.

A console forgoes a lot of that background stuff, and limits the hardware compatibility issues by being a fixed environment. Your game only needs to run on one specific combination of hardware for each console it's released on. In that sense, it is a lot less finicky than running it on a PC.

You are talking about hardware deficiencies more than anything, you can get those on PC too if you just run low-powered hardware. I'm more talking about bugs. Maybe it's changed since I used Windows years ago, but I remember having issues from time to time with PC games. Crashing, weird behavior from alt-tabbing, some games just running at low GPU usage for no reason even though framerate is uncapped, and various glitches. There's a reason there has been a growing interest in sandboxing for software with docker, etc. Software is deterministic, if you give it a consistent environment it will do the same exact thing every time.