Ok.
A. My party spent their Devil's Luck to survive. They didn't spend it to hit and do big damage. Maybe they could've been more offensive and reckless. It would have at least ended things sooner, for good or bad.
B. The adventure didn't provide any stats for folks to help. If that should've been an option, it could've been listed. (In fact, I couldn't find anything suitable even in the entirety of the Start Set box.)
C. Yeah. I could've had the Pirate Queen go with them. It wouldn't have helped....
***Because the problem is with the inherent design and math behind Pirate Borg. The odds of hitting. The amount of damage done per strike. The bloated HP of the enemy. Which is the whole point of this thread. The math doesn't work for the kind of game it's trying to be.
The quick starter adventure provides stats for the Pirate Queen (p. 7) and for regular pirates (p. 13), all of whom could help. There is also a QR code for a random PC generator that could create NPCs on the fly. If you have the starter box, then the included adventure (Trapped in the Tropics), then that includes three types of soldier that could be reskinned (p. 15), a marooned pirate stat block (p 18), and a couple of named NPC stat blocks (p. 29). So there are lots of options to help.
Now the big bad with his 66 HP is a tough opponent. It's not meant to be a fair fight for four level 1 characters - it's likely that they will get killed, and added to the Ghoul Lord's retinue. It won't even take very long since
he can attack 3 opponents at once in melee and will likely drop a starter character in one hit (again, barring devil's luck). Two to three rounds tops. Which is fine. It's fast and easy to create new characters. It's a learning opportunity for players to OSR games that they need to approach this opponent differently with their new set of pirates.
So say the new PCs don't rush in by themselves and look for allies. They engage in some roleplaying and somehow recruit a crew of pirates (say 8) to avenge their earlier PCs, and they make sure that everyone has muskets. It's pretty old-school to gets lots of hirelings. They now lure the big bad out of the fort (he doesn't stay in the final room of the dungeon and sometimes even wanders into town as a random encounter), and ambush him on the dirty streets of Tortuga. 12 musket (2d6 damage each) volleys ring out from rooftops and alleyways and windows! At an average 7 damage each, 50% hit chance, that means 48 damage right at the start (18 hp left). The muskets will take a couple of rounds to reload, so the PCs might need to finish their foe off before he escapes (none of our hired guns are willing to risk getting into melee). The fight is still dangerous and possibly fatal to some, but will likely only last a couple of more rounds. It's a great sendoff to a nasty foe. They then steal a ship with their new crew and seek out riches and glory! The end.
Now, the quick start doesn't include rules for the swivel guns, cannons or gunpowder casks, but most GMs could probably extrapolate something (e.g., if a musket does 2d6 damage, then a swivel gun could be 2d8 or 2d10). The starter set does include rules for bombs and using cannons at PC scale (x5 HP damage).
Math seems fine to me.