LOL....
To try it out is SIMPLE!
Take a 36v ebike with regen (gives about 36v 6a or close to your 14v 21a) and while it's regenerating, try to pedal, you'll realize FAST, that's it's not so "easy".
P.S. I watched that second video... LOL.
You see that setup.. He's using the ENTIRE CIRCUMFERENCE of that wheel to generate that amount of power... It's like using a 80t to 5t crank..
Can't wait for you to try and report back your findings...
P.P.S. I will stand by my original statement.. (with a small addition)...
If pedaling using a generator would produce a usable amount of energy EVERYONE (who uses E-BIKES) would do it.