All those factors can be addressed with a small hub motor and battery which together is much cheaper than the high-efficiency parts. If you set the power level right, you could even tune it to give the same reduction in effort for the rider.
Batteries and motors are more energy efficient than humans, so it's good from a more pure energy point of view too.
To me, that seems to add a lot of weight, cost, complexity, maintenance (battery charging and replacement), and failure modes (running out of juice) when you could just spend a couple more bucks for a lighter bike that's also more fun to ride.
Also wind resistance goes up as the square of velocity so it's harder to go faster than it is to simply ride around a clunky heavy bike.
There is a saying in cycling: strong,light, cheap. Pick two.