Read through the overview and the introduction and literally could not tell what Overmind was supposed to be helping with. Everything shown looks like just basic examples of using state normally in JavaScript. What does it actually do?
If you need a general state management library you'd be crazy to write your own. You might be able to do 90% of what the big, popular libraries have done, but that's just settling for something 10% worse for no good reason. Why give up all that knowledge, testing, and creativity when you can build on top of it? Let other people make the mistakes.
In general CS course I took in Uni over 20 years ago, one learns about data structure and state of an application with multiple threads. It is something 'web developer' lacks as web was originally meant to be a document based.
I am not saying developers can't pick that up during their development career, it is just that the bar for being a developer has being simnifically lowered in the last few years. It turned more into a buzz word now days.
This is unrelated but it's something that annoys me. Even in Tim Berners-Lee's original memo proposing the web he stated "Hypertext allows documents to be linked into "live" data so that every time the link is followed, the information is retrieved. If one sacrifices portability, it is possible so make following a link fire up a special application, so that diagnostic programs, for example, could be linked directly into the maintenance guide."
The idea that the web could be about more than static documents was there right from the beginning.
[1] https://www.w3.org/History/1989/proposal.html - Live Links section
Also, have you taken a look at the source code for Redux let’s say? It’s an extremely small library. Not exaggerating, it’s on the order of 1,000 LOC. You don’t think someone could produce that?
I would agree with what you’re saying if you were talking about something like Postgres, which is enormous and complex. These state management libraries are very very simple (I’ve implemented small versions of them many times), and really just encourage a pattern in the code. They’re not operating systems unto themselves.
There are numerous other discussions on whether use of a state management library is needed ever, or at least in some projects. As someone who doesn't usually actually need it, I can understand the motivation for less people to use it until they know enough to realize they need it, but also don't understand people who ignore valid needs of larger teams and projects where something like Redux makes a lot of difference and is necessary. Again, unless those people consider themselves and their projects to be the biggest and most complex that can ever be, which is very likely to be false.
That wheel might have been designed by a team of brilliant engineers and built with the latest super materials, but if it's a race car's wheel I wouldn't mount it on a bicycle.
I feel like you could take this stance on almost any framework or library.