Your post is excellent but IMO the sarcasm about statically strongly typed languages detracts from it:
You and @sodapopcan (to whom I already gave an example about what they bring to the table 
but he still seems to wonder what are they good for) seem to underestimate the ability to refactor via a checklist that the compiler is literally handing you, as opposed to crudely searching for certain texts in the codebase and assuming that’s enough – and to be fair to all sides it usually is, which makes the cases where it is not enough all the more dangerous and confusing (some codebases pass modules around and use them dynamically, others use protocols, yet others use apply, and let’s not even mention those that import or alias stuff so it’s not trivial to find even for LSP sometimes etc.).
That, plus the ability to strongly statically type and enforce data structures in important places – like configs, a good amount of which are a trap in Erlang land, a mish-mash of nested keyword lists, just lists and various tuples – actually saves time. I already gave example to @sodapopcan about HTTPoison / hackney and a few others whose e.g. SSL configs are one of the things I’ve seen people get wrong no less than 50 times in the last 7 years and a few months I’ve been contracting with Elixir.
Also you’ll need to clarify on the “can’t adequately test” part because for years of writing Golang and Rust I am just not seeing that to be true.
So I propose: let’s argue OO vs. FP without sarcastic jabs at the expense of static strongly typed languages because (1) it’s a different discussion entirely and we’re muddying the topic and (2) I don’t feel that most detractors have made an effort at understanding “the other side”.
I’ve been at both sides and while I agree static strong typing system won’t add much value to Elixir in particular because pattern-matching already allows you to both assert on data shape and the types of [certain parts of] it, I would still posit that some better typing system will reduce certain commonly happening WTFs per minute and will especially remove a whole class of deployment problems where you have to make a release (or force-rerun of a CI/CD action) just to curse “frak, where is that keyword list value supposed to go in the config of this library exactly?”.
