Well not exponentially, but could easily be 4-8x the size. Compare a Leica 35/1.4 with the EF 35/1.4. (I use a Leica 35/1.4 on my R as my main lens now.) The EF is twice as long, and twice as wide and twice as tall making it 8x the volume, and on top of all that it's not even that sharp wide open. (Hilarious coma in the corners.)

Sure, you can cherry pick some examples. So can I...

Leica APO-Summicron-SL 35mm F2 ASPH for Panasonic/Leica MILCs – 102mm (4”) long, weights 720 g (25.4 oz)

Canon EF 35mm f/2 IS USM for Canon DSLRs – 63 mm (2.5”) long, weighs 335 g (11.8 oz)

The Leica is nearly double the weight, 60% longer, and has 40% more volume (your 8x figure is wrong, unless you’re talking about the boxes the lenses come in...lenses aren’t cubes) and on top of all that it doesn’t even have IS.

And 35mm is a focal length where a shorter flange distance

*can* have a big impact (unlike telephoto designs, for example).