Proper exposure affects other things but not sharpness. Shoot RAW, expose to the right, and all will be good.
Incorrect exposure increases noise and thus affects perceived 'sharpness'. Exposing to the right also, from my testing over many years, is, in effect, often incorrectly exposing the image (or effectively parts of it to be more accurate), and depending on specifics can have a similar effect to incorrect exposure in that noise levels can marginally increase in some areas. I am an advocate in shooting 'within latitude' and this 'latitude' needs to be assessed for each camera - some have greater 'latitude' in terms of exposure than others. All that said, choice of apertures, movement (even with flash/strobe illumination at times) and precise point of focus are usually more significant.