That's OK, as our missile defense system was never designed to defend against the kind of massive attack we would expect from the Russians. It was designed to defend against a minimal missile attack from a rogue state or non-state actor.
That's how I always looked at it. A small attack from North Korea or Wherever-stan would be worthwhile to try and stop. No matter what ruinously expensive changes in their weapon hardware they made, a comparatively inexpensive software or reconfiguration could cope with it. We stay safe, they go (more) bankrupt.
Russia though? They punch a heck of a lot harder than North Korea, and not much is going to change that.