Short answer
Hire an architect when license-backed design responsibility and complex coordination matter. Hire a residential designer when you need practical layout/design help and the project does not require a full architecture engagement.
Architects carry a different responsibility
A licensed architect can lead design intent, coordinate consultants, and take responsibility for architectural work where licensing matters. That does not automatically make them the right answer for every remodel.
Designers can be the pragmatic choice
Residential designers are often faster and more budget-aligned for kitchen reworks, interior layouts, modest additions, and owner-led projects where the design problem is contained.
Ask who handles the permit set
The clean test is simple: who produces the permit drawings, who responds to city comments, and who brings in engineering if needed?