hp,ergs,newtons,watts are all expressions of power so yes you can calculate these things with ease.
the 200 watts as expressed in a test is the amount of power that the subject produced…period, gears on the output if anything because of frictional losses reduce actual system power (ever see gearing on a dyno or a water turbine, or any power producing system…no the reason is that gearing no matter how efficent consumes some power though friction).
Gearing is used in vechiles to optimise a power source (motor) output curve to the requirmens or demans of the vechiles operating enviorment a narrow power band motor like a diesle (500-2500 rpm) will have more gears to match its output to the operating enviorment (empty, loaded, flat ground, hills, high/low speeds). A motor with a wider power output (gas) (500-8000 rpm) will need fewer, however for max effiencty such in a raceing car multiple gears are also used to remain in the peak power band.
A human is like a diesle, the cyclic rate or cadence of the legs is quite narrow and so mulitple gear sets are used to maximize the vechiles range of speeds and conditions. The use of gears in “spinning classes” is part a mind game and part it puts a vairialbe low level aerodynamic load on the wheel.
The use of rare earth magnets in your genarator mayl allow you to harvest a higher % of imput power, dont create any more. The higher field strenght and power generation is somewhat offeste by the higher induced magnetic drag (see magnetic brake). This whole thing is called TANSTFAAL"…THERE IS NO SUCH THING AS A FREE LUNCH…check newtons laws.
Your room full of spinners, you have 30 of them all in super good shape and the session is 1 hour you are going to see a total output of less than 6,000 watts how much less is because they for that full hour you are expecting/demanding that they all produce 100% output a full gut buring max effort and that dont happen. Imagine running up a hill as hard as you can being chased by wolves for 1 hour, your going to start out fast (200 watts) and by the time that 59 min is up your at a crawl (20 watts) because of lactic acid build up etc. This is a prime example of why ID’s should at least study some engineering so they dont look like fools to others.