Ah, yes, expressjs, or as I like to call it, "the mutation ecosystem," where who knows what middleware has mutated which object in which way, and whether any state has leaked or whether any assumptions about control flow will actually hold true. Where it's common to see callbacks, streams, Promises, generators, and async/await patterns all thrown together in a mishmash that requires continuous syntactical context-switching.

Honestly I'd rather develop in vanilla NodeJS where the approach is at least consistent, than in the Express ecosystem where sure your problems may have been solved 1000 different ways already but where none of them really fit what you want to do, and where there are many layers of hidden incompatibility that are going to require you to make adapters for each library anyway.

What's so complex about ASP.NET Core web api, other than having to learn to use a DI framework?

I found it very simple and minimal (again, other than the DI) when learning it.

Can you elaborate on the "mind boggling" complexity?

Flask is self-described as a "micro framework", which makes it simple to start with, but IMHO difficult to grow into something bigger.

I like the balance the ASP.NET Core 3.0 strikes.

  dotnet new webapp -o HelloWorld

Yields a fully functional site with * HTTPS * Logging * HTML templating * CSS/JS bundling & minification

And all of this is easy to customize and change.

"Web API" projects are even simpler-- it's just a small handful of files.

Is something like Nancy [0] close to what you're after? I've not used it myself because I prefer the structure of the full approach but from my extremely brief interaction with Express in Node it seems similar?

[0]: https://github.com/NancyFx/Nancy