The idea that a singular man can output a horsepower (~700W) for enough time to toast bread is still very impressive to me!

Clearly an Olympic-level athlete. That being said, I can't help but imagine that with some optimization, it could make the electricity generation a bit easier (maybe more RPM but less torque needed?). Clearly, the video shows him straining and pushing.

Power == RPM * Torque, converting to less torque but more RPM with gears probably would be easier.