In my experience, whatever is typically done by HR and People teams can also be done by a generalist admin team.

- Recruiting - Onboarding - Payroll / Insurance - Culture development - Team building - Legal compliance - Offboarding

We (~120 employees) have worked with some massive conglomerates and retail enterprises too, and HR is wholly necessary for those formats. Where the line blurs between white collar and blue/brown collar collar is where HR becomes mandatory. For a purely white collar company? Absolutely useless and not worth it.