The vast majority of development time is spent finding and fixing bugs. Small startups got huge often because they hit the sweet spot of features before anyone else, not because their code was high quality. Once they get large installed bases (and large valuations) they get religion about the value of more strict typing.

The unknowable question is, would they have hit that sweet spot anyways by engineering their product more rigorously, and had less pain later? Or would it have impeded them in the exploratory phase of writing and rewriting their code until they hit that spot?