I never subscribed to gain ratios.

The gearing of a bike is determined by the chain ring to cog ratios and the wheels have to be factored in as their rate of travel changes according to their size... it is obvious that a 20 inch wheel spinning around at 1 revolution per second will not take you as far as a 28 inch wheel turning at the same rate and gearing adjustments have to be made so a person driving a 20 inch wheel does not have to spin the cranks at ludicrous speed to maintain the same speed as someone on a bigger wheel.

The crank and it's length are just the mechanism by which power is delivered... it is a lever which reduces the amount of force that is required to turn the chain wheel.

Calculating gain ratios is something I do not do as it makes no sense (to me) and feel that gear inches are a very efficient way of calculating how far a bike will travel per revolution of the chain ring.

The delivery of power is not a factor as in the end, it's always about how fast the chain ring turns in relation to the rear cog or cogs and the wheel size that is being used.

The crank lengths in use (and our wheel sizes) are there because these they are what work with a broad spectrum of riders and an average physiology / body structure.