Regarding react, JSX is not a steep learning curve, most of the components are the same markup as their HTML counterparts with the difference being how to handle refs for when you need to manually bind things, and attributes following the JS DOM syntax not the html syntax.

For the most part, JSX is the piece that people pick up quickly. It’s how to properly isolate state management from rendering or integrate as needed that tends to get a bit more complicated. Understanding the lifecycle and event model are a couple other issues as well.