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No, part of it is that (optical vignetting), part of it is digital losses (pixel vignetting, angled light hitting vertical wells), part of it is dependent on the angle of light hitting the sensor (natural vignetting, actually the cosine to the fourth), and of course, if filters or a bad hood block anything, then there is mechanical vignetting:
Only optical (and mechanical) vignetting can be dealt with by Zeiss.
Yes, I have rudimentary awareness of the effect of pixel wells and micro-lensing (particularly difficult for mirrorless cameras with full frame sensor to deal with, with short register, right?), but obviously I'm not talking about that; many Zeiss lenses do exhibit more vignetting on the same system than other lenses do so it's an optical aberration pertaining to the lens optics and design. Even the Otus, although superlative in just abut every single optical quality, isn't more than average in this apartment. Reducing vignetting just doesn't seem to be prioritized for Zeiss.