HRIS at 80 EE — when does it stop being optional?

We're 80 EE, growing toward 150 EE in the next 18 months. Currently on a basic payroll provider + spreadsheets for everything else. No formal HRIS.

For people who waited too long vs. people who adopted early: where's the inflection point where running without an HRIS actively costs you money or breaks compliance? Is it really at 50 EE like vendors claim, or is 100-150 EE more realistic for a competent ops team?