There is a constant game of leap frog. There may be brief periods where missile defense systems have the upper hand, but there will never be permanent safety from incoming missiles. “Pretty advanced” isn’t good enough.

Maybe we should try to build a system that could reliably stop a small attack from North Korea or Iran, but trying to counter Russian or Chinese attacks would be ruinously expensive and could still be overcome by alternative delivery methods (shipping containers, etc.).

Problems facing missile defense systems:

• Easy and relatively cheap to accompany real warheads with decoys
• If we stopped 90% of Russian or Chinese warheads in a full-scale attack (currently we might get 5%) society is still effectively toast
• Hypersonic missiles are becoming smarter, more numerous and faster along with missile defense systems
• Missile defense capabilities are limited by treaty (I think)

https://www.aip.org/fyi/2022/physicists-argue-us-icbm-defenses-are-unreliable