Conceptually is nice. All react code I've seen or wrote of even the most trivial systems have components (and more then a few) that override lifecycle methods - which is by almost definition OO's polymorphism.

Buy even if you could write every component with the stateless style it doesn't change the fact that your framework/GUI-library is using OO extensively and in it's fundamental concepts, I think that makes it OO, you seem to disagree.