As well as in Korea, but it was the PVA in Korea, not the PLA.

https://en.wikipedia.org/wiki/Sino-Vietnamese_War

https://en.wikipedia.org/wiki/People%27s_Volunteer_Army

Perhaps, but the Sino-Vietnamese War is nearing 40 years old by now. A lot of combat experience and grand strategy from then is completely irrelevant by now. Arguing over how much the basic infantry experience has changed from then to now is one thing, but gaining a significant naval and air power when your last major conflict had zero such thing is another.

That's primarily the reason why the PLA shouldn't be taken seriously. They are mechanizing their military with zero real idea what makes them any good.