Yes. The mount’s throat diameter can impose real optical limits.

A narrower mount restricts the size of the rear opening the lens can use, which limits the possible exit pupil diameter. That matters because it can make very fast lenses harder to design, especially if you want good illumination across the frame rather than heavy light falloff. In other words, mount diameter can contribute to vignetting and can restrict how practical ultra-large-aperture designs are.

A larger mount also gives lens designers more freedom for the rear optical group, which can help support more symmetric lens designs. That can influence things like depth of focus and the rendering of out-of-focus highlights at very wide apertures.

For specialized lenses, a larger mount also makes compatible tilt/shift designs easier, since those lenses need extra image circle and room for off-axis movement.

So while flange distance is often the better-known constraint, mount width also matters: it affects rear element and exit pupil size, vignetting control, design flexibility, and the feasibility of some very fast or shift-capable lenses.