[creato]

I agree he could have used some other spring, but I don't think he could have used a weight. The acceleration of springs/rubber is potentially much greater than a weight (at least one starting at rest).

[Robotbeat]

You can use mechanical advantage to get the same result.

[ButtSpark69]

Which means a giant physical structure to support that giant lever arm. When you scale up to things that can knock down castle walls I suspect the difference is incredible.