If you're struggling to fill the gaps or onboard people at a certain point you have to admit to either managerial or organizational failure to adapt. It's called taking responsibility
I’m asking because my experience is largely with <200 people companies (more so with <50) and onboarding and such is always very scant at startup stage and only starts to happen in my experience at stages of intense growth and post series C/D, but I may be in a weird niche.
These things also tend to happen organically at different stages depending on the team but don’t become mandated/invested in until later.