Ballistic missiles can be shot down.
So can cruise missles
Not even close
Supposedly, it’s maneuverable, not ballistic. We have had maneuverable reentry vehicles (MARVs) for many decades, going back at least to the Pershing II, with it’s mach 8 MARV. A high-G maneuvering vehicle traveling at mach 20 would certainly be a very, very, challenging target. That said, Russia has had serious problems with previous supersonic missiles suffering catastrophic failure when attempting the high-G maneuvers required to avoid modern air defenses. Historically, Russia has always over stated the capabilities of their weapons, while we tend to understate ours. If we decided that we didn’t want this ability, it’s likely there was an unacceptable trade off in reliability and accuracy. Or we decided on an alternative technology, like stealth or decoys, to ensure a kill.