I think you may have made some incorrect assumptions in your application of Ohm's Law with regards to "C" rating.
Please look again at what Jim stated above.

You can also run a fairly simple experiment. Take a 25C and 50C 5000mAH battery, both charged to the same termination voltage (say 4.1 or 4.2 ... your preference)
Connect the battery to an electronic load Do this at a reasonable discharge current (say 5C - 25A). If you don't have an electronic load, then a power resistor should suffice (sized and cooled appropriately)
Monitor/record the capacity discharged when you reach your desired termination voltage (say 3.7VDC). You can use an inline wattmeter to do this as well.
Do this for both batteries and compare results.

If your application of Ohm's law is correct, then a 50C battery will always have a significant increase in (discharge) capacity compared to a 25C battery (20% in your example math in your post), independent of discharge rate/output current.