Use the right tool for the job.
"Scale" can be seen under different angles. You can run thousands of boxes with relatively simple code if it's designed to scale horizontally. Twitter used to run on Ruby this way, until they accumulated money and expertise enough to rewrite the whole thing and save on operations and further development costs.
Your code can be millions LOCs and run on a few boxes; it's a very different sort of "scale".
In one company where I worked they had a crazy mix of codebases, from modern Scala down to ancient PHP code. But since it was architected reasonably, it was possible to replace the PHP code piecemeal, without stopping the system. Do the devs that started it 15 years ago with PHP deserve blame for choosing a poor language, or praise for coming up with a serviceable architecture?
You can see the original post as a step in the right direction: in a complex codebase, static typing has a large number of advantages. Barring a wholesale rewrite, how would you gradually transform your code to using it? Yes, by documenting the current state in a formal way, introducing a typecheck build step, then maybe splitting out certain components and rewriting them in other languages, etc. Look at TypeScript.
Unfortunately, there's no way around using quick-and-dirty prototypes at the very early stages, if nothing else, for lack of technical expertise among founders and their first employees. They have business ideas first and foremost. So a tool like that would help exactly the step you want done, switching to a nicer and more manageable stack as growth allows / demands it.