Assassin's Creed 4 would have been the best pirate game ever made if only it weren't also an Assassin's Creed game. Remove the conveluted modern day story, the 30 minute walking-around-an-office segments, the shitty trailing missions, the presence of the assassins and templars. Just make it a self contained pirate adventure story with all the same mechanics, more ship options and maybe some moral/reputation system (honorable privateer vs. bloodthirsty pirate).
Back in the day, as a kid, I played Uncharted Waters 2: New Horizons. The SNES port of a game where you'd sail around the world in the 16th century, playing as your choice out of 6 characters, each with a different story and role: pirate, royal navy, explorer, trader, etc. You'd form your fleet, travel the world, discover amazing landmarks from all over the globe, engage in sea battles, board ships, duel enemy captains, fight the pirates, the navies, or the privateers, trade goods from faraway places, use the market fluctuations to make a fortune, steal the cargo from other traders, sell your discoveries to cartographers, etc. All the while, the paths of the 6 characters meet and diverge, with an interlocking narrative that includes wars between countries, the war against piracy, and the search for the legendary city of El Dorado.
I've been ever since looking for something that'll scratch the itch that game gave me, and nothing came close, not even the later Uncharted Waters games (most of which are shit MMOs and now there's a remake of New Horizons which I think is just a fucking gacha cashgrab).
But Black Flag was close, man, really close.
It doesn't have the mechanical depths of trading and exploring, but it does do little bits of most of what I want here and there.
Of course, the Assassin's Creed shit is infuriating every time it rears its ugly head to distract you from the great pirate game you really wanna play.
The fact that Ubisoft has never put this game out is one of the biggest mysteries of gaming history to me.
The fact that nobody has tried to make a proper game like that after seeing the success of BF is what's baffling. Every attempt is some online live service shit or something.
It's not like pirates haven't had surges in popularity, why not leverage that?
It hurts, man.