This does not prove your point. Annotating a large dynamically-typed codebase with type information is a large amount of work, regardless of the language. This tool makes that easier.
It seems to me it's so difficult to manage such a code base, that they decided to do that "large amount of work" in addition to the large amount of work required to develop the necessary tools!
In which case it seems prudent to avoid the said amount of work by picking another programming language for one's large-scale code base.
> In which case it seems prudent to avoid the said amount of work by picking another programming language for one's large-scale code base
When I first saw Instagram I thought it was nonsense, I was wrong. When the founders started Instagram, I wonder if they had the amazing foresight to see what it would become. I would suggest getting to market was more valuable to them than worrying about what maintenance they would have to do once they had a billion dollars
While I'm a type-adherent in my day-to-day (F# represent, wut wuuut), I think this isn't reflective of the chicken and egg dilemma for startups... There are an immense number of things they "should be" doing at scale that they can't do early because they're relying on their early product to scale. Time to market, and windows of opportunity, are critical to startups.
Any immature technical decision at that part of the lifecycle needs to be made not with an attempt to make perfect forever from the start, but rather with an eye to transitioning to smarter solutions aggressively as you scale up. The company may be 6 pivots away from success, so better to validate solutions in the market than prognosticate.
I don't accept the premise that a lack of typing significantly improves development velocity, per se, but language decisions are about ecosystems, key components, and local talent. Where these companies get into coo-coo land is not integrating those immature components into better systems as they're getting bigger. Next thing you know someone is writing a whole compiler chain for PHP in an attempt to reinvent a sane programming language, or trying to get Python to be Java.
Smart, modern, functional languages provide development velocity and pleasure equal to Python with fundamental type safety and guarantees. But in a world where just putting a button on a webpage means multiple dialects in multiple languages I think we should be ok mixing and matching on the backend to scale smartly.