More fuel, but a bigger wing and more drag, ending up with a much longer transonic acceleration, lower thrust to weight ratio and no greater range than the F-35A. That’s before you add in that it won’t benefit from the proposed conformal tanks etc being looked at by LM for the F-35A.
Thats before you consider the total planned production run of the F-35C is about 320, assuming the USN doesn’t cut its order, as opposed to several thousand planned F-35As, meaning the cost of spares and support will be even more eye watering than the A or B.