Biggest problem in my opinion is the pedal at the top of the stroke. In fact, that can make the longer crank worse than the shorter crank unless you compenaste for this.
The only way to compensate for the decrease in power at the top of the stroke is to move seat forward and higher. (if you don't do this the longer crank is worse IMO)

Like I said before smaller frames already do this via the steep Seat tube angles and long top tubes they have. Look at tall frames? They are the reverse: shallow seat tube angle and shorter top tube. They ain't proportional.

I restate this: You can't apply "proportional" theories to things that aren't "proportional". (Simple)