Why does the US care so much about China's hypersonic weapons?

Example: Gen. Mark Milley calls China's hypersonic weapon test 'very concerning'

If we currently have mutually assured destruction (MAD) where nobody can fire nuclear weapons because the other side can retaliate and wipe both parties out, then why do these hypersonic weapons matter? It just means that China has joined the MAD club. The only practical restriction is that none of the already-established MAD club members can fire nuclear weapons at China.

Neither of the two obvious explanations I can see are very appealing:

• The US was intending to fire nuclear weapons at China, so China's newfound ability to retaliate is not welcome (and China calling the US bellicose is fully justified).
• The US doesn't believe in MAD, and we are all fantastically lucky there hasn't been a nuclear war yet.

Cynically, there is also:

• The US doesn't actually care. Only the US military does, because if they can get the rest of the US to care, they'd also receive more funding.

I am wondering which, if any, of these are the right explanation.