There are plenty of supposed Steam Deck killers available in the portable gaming space, from the Asus ROG Ally to the Lenovo Legion Go and all the Ayaneo and ONEXPLAYER devices in between. But none of them have managed to outright slay the dragon that is the mighty Steam Deck yet.
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.