First, let me note that I'm not trying to tell DPS to not DPS. It's your chosen role, and the role you were asked to play in your group. Do it! Do an awesome job of it. All I want to say is there are also other things you can be doing. These things may lower your DPS, but don't let it halt your damage entirely.
Focus on your utility. Earth Shock and Purge completely lock down some of the mobs within Magisters' Terrace. Purge cripples the Dawnblade Magisters, which can become very frightening if their self-buff stacks heavily. These particular mobs are immune to most crowd control anyway, so the ability to shut these down is fantastic.
Additionally, if you're dropping Windfury, you can 'twist' it with Grounding Totem to take some of the heat off of your tanks and healers. You can drop this totem pretty much every time the cooldown is up, and it will absorb something almost immediately. Very few mobs in this instance don't cast spells. As soon as it's used, Windfury can go back down and your melee probably never even lost the buff.
The usual crowd control still applies, of course. Cyclone to buy those extra seconds. Entangling Roots works in this instance, though most of the mobs are casters. [EDIT: Entangling Roots does not work in this instance, but I am leaving this here so you will see the mistake I made and not make it yourself! My apologies.] Retribution Paladins should remember their new toy, and use it carefully. If you've forgotten, patch 2.4 gave you Turn Evil. Turn Evil can fear Undead and Demons, thus you can buy your group enough time to deal with everything else before worrying about the Succubus trash mobs and some things in the Delrissa encounter.
Those are just some examples. I don't think I need to detail all of a class's spells and what they do. If you're comfortable going into Magisters' Terrace, you probably know how to play.
The biggest thing to stress is that sometimes you need to force yourself out of your comfort zone. Feral druids love being cats, Balance Druids love being Moonkin. Retribution Paladins like hitting things, and so do Enhancement Shaman. Elemental Shaman zap the heck out of things. It's just what you do. Most people are content with this comfort zone. They play their spec rather than play their class. You know what? Sometimes that's okay. I would say that it's okay most of the time. However, the last two bosses of Magisters' Terrace do a little bit to force you out of that comfort zone.
For example, Priestess Delrissa and her friends cannot be tanked and have no threat tables. Protection Paladins and Feral Druids may find themselves dropping heals instead of tanking, or cleansing, or DPSing. Although, Prot Paladins are not exactly the #1 choice for dealing damage.
Kael'thas is similar, depending on your strategy. His first phase is straightforward, but his second phase is pretty different. For one, doing damage during Gravity Lapse is optional. For two, he doesn't need to be tanked. Since he doesn't need to be tanked and everyone takes a steady DoT during Gravity Lapse, in addition to potential accidental hits from the purple orbs of doom, hybrids may consider helping out on healing until Gravity Lapse ends. While not necessary, you would be amazed at how much a few Feral Lifeblooms or Enhancement Chain Heals can help.
The Comfort Zone is not your friend. Be a hybrid to the best of your ability. Though you may want to keep spammin' that Moonfire, it isn't always going to be what is best for your group while the community is adjusting to this dungeon. Most of the dungeon, you'll be just fine doing what you like to do. It does have those moments where you need to step up, though. Do things a little differently. Make Magisters' Terrace easier for everyone. Hybrids have the power to make any difficult encounter seem fantastically easy. Use that power.