That said, two of our best junior devs (at Arist YC S20) are Lambda School and Ironclad grads respectively, and neither of them had any background in programming and went right from bootcamp into their current positions. So it definitely works for some people.

Isn't that just a case of some students having natural ability where a large percentage do not? If being a good developer was only about knowing syntax and writing efficient algorithms boot camps would work fine.