The Iron Dome performance is indeed a superb demonstration of what can be achieved. The large number of simultaneous intercepts out of a single defense site is an awesome achievement. Thats a lot of radar tracks. This is a partial answer anyway to the decoy response.
There are scaling problems though when it comes to MRBM’s and ICBM’s. Distances are much greater, radar coverage is harder to provide, speeds are much greater, and all of these come with greater lag times in response, etc. The problems are not that the theory is wrong but that the engineering is harder. Interceptors for ICBM’s will also have to be nearly as large as ICBMs, just as capable, and probably more expensive per round.
It would be enormously expensive to provide a system that can significantly reduce the damage of a full launch from Russia. It is much less expensive to provide a system that can stop “rogue” or small scale launches from a smaller power.
“It is much less expensive to provide a system that can stop “rogue” or small scale launches from a smaller power.”
Existence of a defensive system, whether it works or not, may discourage “rouges” from attempting some types of mayhem.
Good point about it being much harder under those circumstances.