@capnswayzjones Congratulations on your faction levels.
Frankly I'm 25/37/15 and have more than enough experience traveling to all of the islands numerous times. Usually going from corner to corner. So please, spare me the "you're new to the game" attitude.
Having bad luck with chests (or any loot for that matter) is disappointing yes- demanding a rare chest because of it? Petty.
I typically refrain from the gold hoarders quests, because there is little challenge within them (with the exemption of riddles). That being said, I have never had a castaway chest from them- not because I "haven't been playing near enough". I simply require more stimulus to truly enjoy SOT than- Travel to island B, and dig up treasure X. Continually. Riddles add so much more depth than a map with marked X's ever could.
The premise of any game is to enjoy the experience that you make for yourself. If you choose to spend all of your time playing grinding gold hoarders missions, using SOT purely as a "time based loot game", then I can see the frustration timely quests for a castaways chest.
But I'll advise instead, that you'd be wasting your time.
The SOT experience largely depends on other aspects such as puzzles, adventuring, and other shenanigans that simply grinding for gold/pirate status cannot offer.
Which is the point I think you are missing.
Nothing currently will give you an advantage over the next scurvy dog. So playing solely for loot is a momentous waste of time (weather the chest you get from a riddle is a captains or castaways), when you could have been having a one-of-a-kind experience instead.
It's the adventure you make it to be.