I have 60 hours in the past 2 weeks just playing organically with varying goals in mind both solo and with friends. There have been 0 Horns and around two dozen Bone Callers.
If the HoFW is supposed to spawn in shrines, I visited several and have not seen any. If they are supposed to only spawn in once per shrine, then the number also doesn't make sense. The Sunken Kingdom category's biggest grind is getting 30 Breaths of the Sea, as coral bottles are something you have to actively seek out.
250 of any loot item is a non-insignificant amount of loot. The Hoarder of Barnacled Gold commendation requires the player to sell 300 Shipwrecked Chests to the Gold Hoarders. This commendation was a stickler for a long while, as progress was not counted if you mass-sold your loot to the Reaper's Bones, as most people with significant access to that kind of loot would. So it required you to be thoughtful about your loot and sort your Shipwrecked Chests away from the rest of the pile. It was ONLY a stickler though. The thing is, most bulk-sell loot commendations complete themselves through simply playing the game. Sure, you can expedite the process by focusing on a specific playstyle, but inevitably if you just kept playing you'd eventually sell as many treasures as you needed to achieve most bulk-sell commendations. Other stickler commendations include Black Powder comms, Cursed Chest comms, and Reaper Emissary Flag comms to name a few, as they all require you to make a decision you most likely otherwise would not do in order to chase them out. You might complete them naturally over time, but let's be honest- how many people keep kegs on their boat just for the sell value after the first or second time they get burnt by them? Still, these things happen eventually. So long as you are willing to take the risk you'll find plenty of kegs on forts, spot the occasional wild cursed chest and (now) even have voyages to hunt them down, and you'll also start remembering to put up a Reaper's emissary before you sell your flags. These things happen. Huge monumental tasks that happen over time. However...
If my current time:HoFW ratio is to be relied upon then this game's originally planned 10 year live service model will have ended long before I achieve this commendation naturally. So, what if I grinded it out?
Is that fun? Is there purpose to that gameplay? Is it something I can do while I pursue other more rewarding or fulfilling commendations/gameplay?
Well I guess I don't know. I haven't tried to grind out the HoFW. But give those questions some thought for yourself. You'll have plenty of time for thinking while we roll this boulder up that hill again.
Oh right the Breath of the Sea comparison. Okay so you have to actively hunt down 30 Breaths of the Sea, right? And that's something pretty much HAVE to actively seek out to do. You don't just accidentally pick up a coral bottle and then accidentally sail all the way over to the specific shrine listed on it 30 times. The gameplay loop is comparable from what I've read though- Go to a specific shrine that you know has this specific item, pick up the one item you need and maybe the rest if you want, and then rinse repeat X times.
So why is one of them functionless and you only need to do it 30 times and the other incredibly cool sounding with lots of utility that you need to do 250 times and is arguably just as rare if not moreso? Intuition tells me that with a bigger sell requirement and more interesting gameplay mechanics it would at least be as common as an Ashen Winds skull. I've probably collected a dozen or more of those in the past 60 hours from doing voyages, forts and other events. Wouldn't Rare want us to play with the shiny new toy after all?
Something smells funny about it.