Indeed! In your dealings with an agency, you might only have one designer working on your project. But (unless the agency is pretty bad) they should be getting input on their work from other designers (especially more senior designers in the firm). And if you really dislike their work, the possibility should exist that the agency will draft a different designer in.

Connecting users to a single freelancer isn't like being an agency. It is valuable, for sure - but agencies offer value in a different way.