Ok, fine if its designed to shoot down opposing aircraft and drones, However with the Russian's putting a ton of money into hypersonic cruise and glide missiles, and the threat of ballistic missiles I don't know what they're talking about, and the cost of a billion dollars sounds like its coming out of their a$$es.
Right now there isn't a defense against Hypersonic cruise missiles, they fly low intelligently maneuver and at hypersonic speeds so Radar warnings are going to be sketchy at best, and there's not a missile out there that certified as a counter. Instead the US is experimenting with "Lasers". as a counter.
In terms of Ballistic Missiles, they are incredibly fast in the terminal stage (roughly 25,000 km/h, so they would outrun an exploding SAM), so frankly most ABM's are built around mid and early course interception.
A good article on what's labeled as the Complex Air Defense system
https://www.csis.org/analysis/comple...ssile-threat-0
A look at the issues of ballistic missile defenses
https://blogs.scientificamerican.com...ssile-defense/