That sounds like a try-hard simplification. Input-process-output is pretty much a generic metaphor for programming in general. I don't think React has anything like monadic encapsulation (not that a language like JS can conveniently accommodate it). You're observing a few high-level properties of a given paradigm and extrapolating an inferred architecture solely from those points.

In fact, you're equivocating the entire management and abstraction of mutable state as an inherently "functional" thing, which it is not. OO is just as much capable of factoring state as a virtual resource that you explicitly make transitions to and from and transparently or visibly share increments across object boundaries, as this is exactly what e.g. Self does with Morphic, right down to the same event handler structure. Just because one is a lambda and the other is called a method doesn't make a huge difference.

I'm saying that just about all of React's insights were done previously almost verbatim in thoroughly object-oriented environments. That some FP evangelists have a kneejerk hatred for it doesn't mean the mental gymnastics for insisting one over the other is necessary. They can be complementary.