That's a good point, but we both know that any ship of any importance was escorted by other ships, and you can't exactly "blend in" with another fleet.
Taking on other kinds of stealthy chenanigans, like hiding on board between the crew before striking could be very tense and memorable, very assassin like but not exactly taking advatage of the whole naval combat mechanic they are so excited about.
Cool nonetheless, though, it reminds me of Dutch naval battles against the Spanish or English, now those were both pirate like and had quite the incredible feats pulled off to gain victory.
If I could spend an AC game by the side of Piet Hein or michiel de Ruyter I would definately check this game out.