Under ideal situation, I think naval power in general should be beefed up like this:
1) Naval unit should blockade coastal cities easily, if you have a hostile unit in your city radius, no watertiles can be work on, access to all water resource from that city will be cut and all water-based trade route will be cut.
2) Transports should hold 6 or more units, carriers should also hold 6 or more fighters, buildings lots of transports and carriers is annoying
3) Bomber/fighter should be allowed to destroy roads, so we can cut off enemy reinforcement routes
4) There should be a topedo bomber unit, that can attack only naval targets, including subs. Should have some chance of sinking ships.
5) All ships should have some anti-air capability, expect subs and transports
6) There should be tactical nukes, cheaper than ICBM, but can be launched from subs, or combine with a bomber.
7) There should be cruise missles, which can be loaded unto and launched from ships. Cruise missles should have a chance of killing both land and sea units.
8) Naval unit should be able to bombard both city infrastructures and units.
9) Better resource destribution, meaning, if you don't control the whole world, you won't have all the resources, therefore, making a navy and proper diplomacy more important.