I agree carrier can be good if invading somewhere a long way away like across the Pacific Ocean. For me its partly the opportunity cost that makes a carrier not seem worthwhile. By the time I have researched them and built a level 5 shipyard, then make the air wing, its ends up a huge amount of resources that could have gone on a seriously large amount of other units.
IMHO the aircraft carrier seems kinda situational at best. Very expensive and can get wrecked easily by other warships/subs. Furthermore planes do not perform very well vs ships. Am I missing something with carriers?