Depends on the lens really, a Super Takumar 50mm f/1.4 will happily compete in sharpness at f/8 (if I take well lit photos with mine it becomes the 24MP sensor that is the limiting factor in detail), but will indeed be significantly less performant at f/1.4. Even a decent Helios 44m will create gorgeous and impressively sharp images.

These lenses stopped down are better more for artistic photography as they have interesting bokeh patterns and lots of character.