I'm not educated enough in this area to have any expertise, however, in my personal experience leaving a lithium-ion battery plugged all the time results in scary semi-exploded batteries that also stop working.

Would you say this is a chemistry/QA problem? Have there been advances in battery / controller technology that achieves the above?

Yeah I was about to say the same thing! I leave my steam deck plugged in all the time (it is my main computer) and the battery still popped (valve replaced it for free ofc)