Sacrosanct
Legend
I don't even think it's over-simplified. It's a very particular approach to damage that has a lot of built in plot armor and very much represents the kinds of stories that inspired D&D in the first place. It's very pulpy, and it makes for very durable heroes. Is that super-realistic? Good heavens no, but it was never supposed to be. Lots of other systems have more 'realistic' damage systems. Even the HP system as written can be massaged in a number of more 'realistic' directions for a DM so inclined. However, that fact that the HP system as written ins't a hyper-realistic model of vaguely medieval combat damage isn't a flaw, it's a design choice, a design choice people can agree with or, and use or not.
People have been trying to make the HP system more realistic since the very beginning, with an article in Dragon about once a year. Introduce pain mechanics! Introduce lingering effects!
None of those ever stuck or even took a foothold. I think there's a reason for that.