My two cents here. Yes not only does the cyclist on a DF bike push down on the crank with his weight, but if standing he has extra push by pulling up on the handle bars. If he does not pull up, he can only push down by the amount of his weight.

Then there are the bent riders like myself. Depending on the design of of a bent or trike, the bent rider can use their leg strength to create torque plus being able to wedge himself between the pedal and the back of the seat.