I would rather the complexity live in a third party library with an extremely simple public interface than have it live in multiple 1000 LOC of vanilla JavaScript that's laid out however whoever wrote it felt that day. You couldn't pay me to do frontend without React - the developer experience is absolutely terrible.
It is a dogma that React has an "extremely simple" public interface. It's got two different flavors of "components", "lifecycle hooks", "synthetic events", "prop types", and more that I'm missing.
Why do you assume that vanilla JS code is terrible? Is it because the average developer can not be trusted to write competent code without the conventions of a framework? If one cannot write competent code without being completely dependent on frameworks, I wouldn't trust them to write code at all.
