So long as these interceptions have to rely on physical ammunition and all of the limitations that entails the attacker will always have the advantage. If you can only launch X number of interceptors even if you have a 100% success rate all it takes to defeat it is launching X+Y missiles and you know Y number of missiles will get through. And since simple missiles are always going to be cheaper than expensive interceptors you’re almost guaranteed to be able to defeat defence systems provided you have the capability to launch enough rockets