What you see as a nightmare is really straight-forward code from another perspective. It just looks very unfamiliar. Yes, it feels raw, it is verbose, it's imperative and not declarative, but the entire app lifecycle is there to see.

You can easily tell what every function is doing, including the library ones, and magical behaviour is kept to a minimum. It could be easily maintained 20 years from now, as you have a very thin layer over DOM manipulation and Backbone itself can be grasped and maintained by a single human.

One could argue that React leads to better development velocity, but from experience I can say that reality is not that simple. The initial speed boost quickly fades, instead a huge amount of time starts being allotted to maintenance, updates, workarounds, architecture and tooling as complexity compounds.

I do not want to work with all the untyped strings and random class selectors. I'd say the code is easy enough to read but nigh on unmaintainable.