But that's exactly the point. According to Sheldon Brown's gain ratio theory losing leverage can't defeat the "gain" because it is the gain!

However, it doesn't make any sense to me because, as you say, shorter cranks promote higher cadence, which is exactly the opposite of higher gears which promote lower cadence. So how can the prolific Mr Brown have come to such a conclusion? Low gearing a pedal strike can both be problems for folding bikes and if Sheldon Brown's gain ratio theory were correct then shorter cranks could help with both, but it just seems wrong on the face, which is a difficult pill to swallow given how knowledgeable and experienced he was.

Now I know 135mm cranks is an absurd exaggeration, but the real question is can shorter cranks be a suitable substitute for larger chainrings? For example, if one wanted to reduce pedal strike and moderately increase the gear, would a sensibly shorter crank kill both birds with one stone?