[whstl]

"but it's usually in the company's interest to also be training more pros"

That's not really my experience.

The reason companies hire lots of people is not because of bus factor, but because they're trying to "make 9 women give birth to a baby in 1 month".

The fact that development doesn't scale linearly is very well known to developers today, but product people barely heard of Mythical Man Month.