I see. We do have good systems, but too few to be of practical relevance in most threat situations.
The North Korea case shows that the step from having one missile to having 100 is extremely short compared to going from having no missiles to having one missile.
I don't think that's a consensus view? Jeffrey Lewis says the opposite,
- "The point is that North Korea is clearly aimed at overwhelming the US missile defense system in Alaska... At that cost, I am pretty sure North Korea can add warheads faster than we can add interceptors."