To add to this, as a senior employee, bringing someone junior up to speed to the point where they can make actual contributions is a big consumer of time typically. Less so for employees who come in at medium rank but even then there is a hand holding period as the new person gets used to the company culture.

In a sufficiently large company you could have a specialized onboarding team, but you’d need to be careful that the specialized team doesn’t get isolated from the technical culture and needs of the rest of the company