So you admitted in your post that you aren't performing well.
Why should bosses die for you again?
Umm because Bioware hasn't added a frikin combat log or interface mods, so we can't tell how much dps we're doing? It's possible that some ACs have too low dps to even beat the enrage timers, even when played right, like vengeance juggs, for instance. We just don't know, and we can't know without damage meters. So either they need to add combat parsing, or they need to get rid of enrage mechanics.
There is no way to improve dps when you can't see whether you're improving. It's like a teacher trying to grade a class with no tests or assignments.