I don't think this is true at all. Nothing about my experience suggests this is the case. There's a very specific stage of startup that usually has little use f

I don't think this is true at all. Nothing about my experience suggests this is the case. There's a very specific stage of startup that usually has little use for Jr. Devs - growing from seed to A round requires onboarding experts. But going from 0->seed or seed->validation or A/B round -> larger round or IPO requires lots of Jr. Devs.