Submarines have nukes, carriers don't. Unless your operational plan is to go nuclear then the submarine represents a single conventional weapon system against land targets and therefore a single point of failure. A submarine lacks flexibility in the roles of air power it can project -i.e it has missiles that have limitations across a target set that demands full-spectrum treatment.
The carrier is an overt, visible sign of deterrence and coercion with a large air force of its own.
I think that's more powerful than any submarine, unless we've now resorted to defining power only kinetically and purely in terms of megatons of equivalent TNT!!!