The complexity, the feature sets, and the move more towards FP-land came later. There is still a pretty straightfoward path to using React rather simply as your UI library.
If you don't get why it became so popular, it just means you haven't had to use much JavaScript to develop apps for at least a decade.
Actually quite the opposite is the case. I was happily writing loads of vanillajs, tons of Angular(1) and wrote several years codebases in emberjs. Besides that I worked with Vue and yes also React once.
React brought nothing to the table that was helping me ship faster and make less unimportant decisions. Back when I had to touch react every week there was a new flavour how to handle routing, state, validate forms and sync to the backend. Ember and Angular had a good default there and were not harder to use.
(Nowadays I tend to stay away from fat js frameworks but mainly because I went indie dev and need to be resource efficient building full stack apps with Rails. But that is a different story. And yes I worked with Go, Python, Java and C# in the backend too.)
In either case, kudos to you for actually enjoying the early days of using Ember 1 and Angular 1. I only look back on those days in horror.