Before switching to React in 2015 I worked with ExtJS and Backbone, and both of them were much harder to reason about. Oh, and GWT too, that was a nightmare.
I guess different people have different affinity and skills for reasoning about different things. If I knew I'd have to work on react for the rest of my career, I'd find a different line of work, specifically because of how difficult it is for me. Things I've found easier to understand than React include AlpineJS, Solid, Vue, Knockout, and vanilla imperative JS. The only thing I recall ever finding more mind-boggling than React has been Sharepoint-as-an-application-platform.
