I'm not sure why one would ever use ADTs for the situation you described, I totally agree it's not a good fit, but it's not what they were designed for anyway. But based on what you've described either a plain StringMap, or if you need to store different data types, a GADT with different type constructors for each of the types which might be present in the data that you want to work with (i.e. String, Integer, StringMap, List, etc.).

The StringMap is trivial, and the GADT requires declaration, but is straight-forward pattern matching/construction from that point onward, so I don't think either option impose any "real" additional cost here.

Navigating/extracting datastructures via lenses or recursion/pattern-matching is clear and concise, definitely not onerous by any means.

I'll gladly admit that my argument hinges on using a state of the art type system, but in my opinion, if we're going to debate the merits of static typing, then we should be looking at the best it has to offer. It seems like perhaps you haven't had an opportunity to work with Haskell or something like it (want to be clear that's not a judgment statement, and I'm solely basing this on your last comment, if you have, sorry about that!), which is fine, I mean, I only ended up learning some of it due to diving down the rabbit hole of type system research while designing my compiler - but if the first thing I had to compare a dynamic language to is Java, then yeah, it's no contest I would use Clojure instead.

I think something important to remember is that I don't think one should be a "static typer" or a "dynamic typer" - dividing the world into right/wrong, good/bad, black/white is almost always the wrong point of view. If I'm automating something, or doing some exploratory programming, I'm probably going to reach for bash/python/etc.; if I'm writing a command line tool or simple service I'm probably going to use go; working on a concurrent system, I'm probably going to reach for erlang/elixir/go/pony/etc. - but if it's even remotely complex, I'm always going to favor the option with the best static type system, because I know it's going to help me (and anyone else working on the system, especially newbies) keep things sane. Over half of what I just listed do not have static type systems, but I still have a clear preference - it is possible to use the right tool for the job without compromising your ideals. Part of why I started working on my own compiler was that I wanted to design something that both provided the strong type system, while still functioning well as a "get shit done" language, something with the concision of Haskell, but the flexibility of ML (permitting both functional and imperative paradigms), a comfortable FFI, and good tooling, including the ability to run scripts interactively (for example, via shebang scripts). I haven't found a language that mixes all of that together in a way that satisfies me, which is why I still use a variety of languages for different tasks. So I guess what I'm saying is, try not to divide people into two camps - it's possible to live in both at different times, but still prefer one or the other :)