You're a privateer hmm. Well here is what you do. You take in your highest level buccaneers to go into battle with you. IF you notice there are two barrels that can be broken and serve as a shortcut to deacon. now use what ever powers you have that deal damage in a large area to destroy these barrrels and damage anything that's behind it.
Now you just make your buccaneers halt the advances of the armada so that they don't that opening you just made. now since you're a privateer, just cast all powers ups that you have to enhance your buccaneers. mean while you're doing that, just keep attacking deacon with all your ranged powers as your buccaneers prevent all armada marines from advancing and taking most of the rifleman hits. Keep this up and as soon as your buccaneers and your traps and powers make an opening large enough for you to slip by the armada robots and get to deacon you go through and start using melee / pistol shots at him. Just continue hitting him until he dies. If ithis doens't work you did something wrong. Hope this helped.
Dear Emily -- yes, my Privateer Charlotte didn't win her first time either (though she did her second time) I don't think your level is unreasonable for being able to defeat Deacon, although finishing up some side quests is always a good option when you are stuck in a hard battle. Some ideas perhaps?
1) Make sure your companions are reasonably leveled up (for instance, at level 37, I would say your first mate should be at least level 35, and your companions you want with you in the instance not far behind)
2) As a privateer, don't run headlong to Deacon and attack him without backup (my swashbuckler Anne's rather heedless 'technique'! Not a good idea for privateers); stay in the back, at least early in the fight, and buff and heal.
3) Use the cannon pointing towards the Armada soldiers: it will shoot caltrops that will damage the Armada soldiers moving in. Just make sure your own people don't step on them.
4) Get a person that wields strong damage to get up to Deacon and fight him. El Toro is good, but he dies easily, so protect him as best as possible. Egg Shen is very good here.
5) Bonnie Anne is very good for backup, to be dealing with the waves of soldiers from the back, and don't forget her heal. You also have a lot of distance attacks that will be good against the Armada regulars.