kbb
Well-known
I disagree with one of your starting premises that "...the big contributor is extremely high apertures....". In many of the modern speed lenses, it's the focus motors. If you are familiar with the XF Fujinon 23mm f/1.4 lens, the optic is about 36mm across at its absolute widest, but the barrel is 72mm in diameter. That optic could be mounted in a barrel smaller in diameter than an ancient Nikon 28mm f/3.5 from the 1970's. But not with focus motors along for the ride.