Any country powerful enough to challenge a US carrier strike group in true, open warfare, isn't a country that is fighting a full symmetric conventional war with the United States. They're fighting a nuclear war.
They are weapons, powerful, effective, government-toppling weapons, and that is what makes them such effective deterrents. For the non-Chinas and non-Russias in the world, a carrier strike group is probably sufficient. If one won't do, how would you like two?
Or ASMs [1] if carrier air or seaspace is breached, carriers are heavily escorted though.
If nuclear deterrence (god forbid) is broken, then I guess aircraft carriers are pretty much sitting ducks.
0 - https://en.wikipedia.org/wiki/Anti-ship_ballistic_missile
If its not a weapon, it can't work as a deterrent, either.
The carriers are deterrents, not weapons. They will be among the first major casualties of any true, open warfare. Carrier-defeating tech has been out for years; therefore they're only ever useful for policing actions - not full, symmetric war.