One interesting thing I verified is that the "1/5 angle input momentum boost" thing Live2D does is absolutely essential to having it behave as designed.
I suspect that behavior is part of what people call the "Live2D physics feel". It basically creates energy from thin air!
So for example, if you rotate a still pendulum by 45 degrees, it will swing over MORE than 45 degrees on the opposite side, because energy was created. Sometimes a lot more. With some settings it'll even loop around!