I think you misunderstand how gear-inches are calculated. They go back to the day when "ordinaries" were in general use. Measuring their "gearing" consisted of measuring the diameter of the front wheel. A unicycle is exactly the same. So your gearing is the diameter of your wheel. An MTB climbing the grade in the video will use the same number of pedal strokes as your unicycle if the MTB's gear-inch number is equal to the diameter of your unicycle wheel. The number of wheel revolutions for a geared bicycle is irrelevant.

I've seen randonneurs riding unicycles with the largest wheel that fit under their butt. Maximum unicycle gearing depends on leg length.