Were you and the end stage of Raven Cove quest? Because that is the only purpose El Patron is there; which is the last stage of RC quest, to give you one of the 3 sword of your choice. If you were helping a friend at the last stage of his/her quest, then El Patron would only fight your friend (even though you I'm assuming you could cause damage - please don't quote me on this, I might be mistaken).
In my two experiences in the past doing RC quests, my friends would only heal me on the side, but I was the only pirate who fought El Patron, and he only fought me back.
I never know El Patron "let us win"; because if we didn't have a healer (for level of notoriety like yours), we could lose against El Patron. And we would have to do it again until we beat him, and that's when we were rewarded with the sword from his treasure chest. However, if we were high level of notoriety, I'd assume we could solo El Patron and win it easily - that is if we waited until the we were high level before we completed RC quest.