No, it's not. An S-curve is logarithmic. It may mimic a quadratic curve in smaller values, but for pragmatic purposes it becomes asymptotic to some arbitrarily

No, it's not. An S-curve is logarithmic. It may mimic a quadratic curve in smaller values, but for pragmatic purposes it becomes asymptotic to some arbitrarily chosen value, in most cases. There is no decay either, because the value of y is still always increasing.