I can vouch for that, not that Cruise Fanatic needs any vouching
Have sailed 2 times in 5A because is the same price as 4A inside. I always pick my cabin though because they are limited and a little quirky.
I have been told by Carnival in the past that an upgrade from 5A is a rare thing, so I do my assignment. Part of the reasoning for it being rare is the next up is 6A which is the starting selling point for standard outside cabins.
Rare does not mean it could not happen. I have had good luck with cabin E-10 on the Empress Deck for same price as Inside Riviera on the Fantasy Class ships. Good luck, and it can be a little bouncy up front but is worth it to me for the view and the deck at that price.