Answering my own question: even the superb Yakhont missile (also a Russian import) is only Mach 2.5
The Chinese can’t have got ramjet missiles working already? Steerable mach 10 hypersonic missiles, yeah one of those would be a problem.
So would a coordinated multi-pronged attack by General Zod and his malignant Krypton horde.
The DF-21 is a ballistic missile, not a cruise missile.
Yes, it can fly at mach 10, but all ballistic missiles of a certain range have to.
The AEGIS system will have a field day with DF-21s.