A template reduces some early decisions
It can suit a small, conventional site when the brand and content fit the available structure. Customisation beyond that structure can remove the original cost advantage.
Custom design earns its place through fit
It is useful when positioning, content, workflows or a wider design system require decisions that a theme cannot express cleanly.
Compare the whole ownership model
Include licences, editing constraints, upgrades, migration, design debt and future page needs, not only the initial build fee.