I have never used the blunderbuss in Adventure prior to Arena.
Nobody did until they revamped the firearms a while ago.
Then the Sea Dogs opened Atena with a huge emphasis to use the weapon early.
Why? Because Rare wants this weapon to be the close quarter option. Making the blunderbuss the best option for ship defence, pretty critical in Arena.
It is also great for pirates interested in learning how to kill other pirates.
It's a great equalizer for newbs versus more experienced pvp'ers.
DeMarco and Lisedi offer the title High Caliber Sea Dog for two-hundred kills.
Sure it's going to be in the back of some enemy repairing a hole, or target locked on a cannon, trimming a sail, or otherwise unaware they're about to get one-shot, but two hundred kills are a dedicated undertaking.
I'll take all the cheap kills I can, these aren't innocents in Adventure, these are Arena spawncampers, or AFKers.
So there are rewards with a pirate killcount for this weapon.
Now that I earned my title, I know what the blunderbuss is for and how to use it.
It's not infallible, or overpowered, it's working as intended, and fulfills a role.