DF-21D is not low tech iskander ballistic missile. It can hit moving targets travel much faster speed.You lack basic understanding of physics.
Iskander is also Mach 10 but easily shot down by the Barak 8 missile system in Azerbaijan, a relatively small missile. Mach-10 and Mach-20+ figures are just high altitude and exo-atmospheric velocities and that too doesn't make them invincible. As soon as their altitude lowers they are much slower, below hypersonic figures, since low altitude air pressure and resistance is much higher and doesn't allow hypersonic flight. In fact at low altitudes it becomes Mach 2 or 3 at best.
Also, a US carrier strike group has more than one ship, and China has yet to prove it's capable of hitting a ship moving at full speed, and yet to prove it's capable of providing accurate, constantly updating coordinates of a US carrier group far away from its shores.
Plus it DF-21D can't hit, we still have DF-17 HGV. Even US admit they can't hit HGV with unpredictable flight path. And don't troll and claim HGV can be shot down. Never proven so far.
Finally, your aegis is tested against a single ballistic missile. Never against a mass like a dozen or more. One ballistic DF-21D cost 1 million dollar. A dozen is only $12 million. An aircraft carrier is $7 billion. Absolutely worth the price tag.
U.S. fails to intercept test missile target
A U.S. warship failed to intercept a medium-range ballistic missile test target on Saturday, the U.S. Missile Defense Agency said.
www.reuters.com