Except for the smallest local businesses, there is literally no such thing as existing manual systems anymore. It's simply not possible to do manual payroll while maintaining compliance with laws, regulations, civil orders, labor contracts, and company policies. Every significant enterprise has either built up a custom automated system over decades, or has customized a commercial ERP payroll module, or outsourced the entire thing to a specialized payroll company.

You could argue that payroll shouldn't be so complex but that's the reality of it today.