Slightly confused - why would the USN not want Dave-C to work? Surely it is the post-Rhino future of manned USN aviation- unless I've very much missed something.
There are several reasons some in the USN aren't enamoured of Dave.
First off it is going to be more expensive than the F-18 and will therefore be bought in more restrictive numbers. There is support for dropping it and buying more E/F/G F-18s instead in the numbers they want.
Then there are those see the EW aspects of the F-18G as being more important than the stealth features of Dave, with some support from the experts who see stealth as a fading advantage as others learn how to defeat it.
There are also those who see Dave B as a threat to the CVN-21 new carrier. The USMC can operate off of the smaller new LHA-R carriers, they are worried that the new carrier will be seen as too vulnerable to NG Chinese weapons and to expensive for littoral operations and will switch orders to Dave B and smaller CVNs at the expense of the bigger carriers. They think if the Dave C is cancelled, so will the USMC Dave B who will have to operate the F-18G for commonality.
You'll find a similar level of support for the RN to go for the F-18 and Cat/Trap on the CVF from some here - who will point out the impetus for Dave B is being driven by the light blue Harrier mafia and not the dark blue naval aviators.....