[Gh0stRAT]

The real way to look at it is via the marginal revenue minus the marginal cost.

Generally speaking, it makes sense to keep hiring more workers if you're getting a net benefit from hiring each one. That being said, at a certain scale the organizational challenges may eat into your net marginal profit. (eg unclear ownership and diffusion-of-responsibility, more layers in the org chart making it harder for decision-makers to hear from the people actually doing the work, longer deprecation cycles, etc)

Hiring is hard and slow, so it's definitely possible that the other companies you used as examples were theoretically understaffed. (if you ignore the costs of hiring, anyway)