If your offers are stable, you are the only practitioner and a standard scheduler handles your appointments, a well-configured template may be the sensible choice. You still need clear writing, accessibility, mobile performance and control of your domain and accounts.
Custom design becomes more useful when the service explanation is unusual, several audiences need different journeys or the brand must stand apart. Custom development becomes relevant when booking rules, reader allocation, payments, reporting or integrations exceed the tools you can maintain comfortably.
We will separate must-haves from later releases in the project scope. The goal is a business you can run after launch, not complexity for its own sake.