> I promise writing applications for the browsers is not challenging.

Yeah it is. I don’t like React but I’ve been doing this since the days of MooTools all the way through Backbone to the libraries we have today. Once your app reaches a certain size and/or reaches a critical mass of contributors it does get challenging and modern frameworks reduce that challenge.

That can be taken way too far. Almost every time I’ve worked with Redux I’ve found it infuriatingly unnecessary. And React is far from the best framework out there. But it is a huge benefit all the same.

Modern frameworks, really components and an API, solve only two business problems: division of labor and training. Knowing that you can address these problems with continuous integration around a common set of rules and requirements.

With regard to application size we fortunately now have TypeScript. All you really need to scale any application is types, functions, and code reuse.