This is a really nifty school project, but… there are two crank arms, so the curve showing inefficiency is missing the second crank that would be present in the real world. And human legs aren’t pistons or simple weights.
The leg itself produces more or less oomph depending on the position of joints and what muscles are active at different positions, when muscles are stretched, slack, preloaded, etc. (Ever wonder why runners crouch just before the starting gun goes off? Or why even little kids flex forward at the hips when racing on bikes?)
The human leg “likes” to stride, pedals take advantage of the way the human leg works. Pistoning like a pogo stick works for mechanisms, but a human doing that is gonna end up as a patient in physical therapy with -at the very least- vicious knee pain from maximally loading the leg with the knee forward of the ball of the foot. (Remember your coach yelling at you to correct your squat form? Compare the “squat” at max load to the leg on a properly fitted crank bike vs on a piston mimic bike.)