I guess it depends on your definition of complexity. Being able to think about your UI as a function of state is a lot simpler than dealing with mutability, coordinating imperative updates all over the place, etc. React’s core idea is simpler than the paradigms it replaced. By simple, I mean as in “Simple Made Easy”[0].
[0] https://m.youtube.com/watch?v=SxdOUGdseq4&pp=ygUQc2ltcGxlIG1...