Excellent comment. What you raised are two important aspects of the analysis that the article didn't bother thinking about:

- how to best leverage the team you currently have

- what is the most likely shape your team will have in the future

Jane Street has enough resources and experts to be able to train developers on OCaml, Nubank and Clojure also comes to mind. If one leaves, the impact is not devastating. Hiring is not straightforward, but they are able to hire engineers willing to learn and train them.

This is not true for a lot of places, that have tighter teams and budgets, whose product is less specialized, and so on.

But this is where the article fails and your comment succeeds: actually setting out parameters to establish a strategy.