This was actually a pretty hard mission for three players at 300, 299, and 297 light. We had to try 3 times before we got it. The first two times we got the boss down but completely underestimated how much time it would take to "mop up" (re: total clusterfuck) the remaining enemies.
Tips that helped us win the third attempt:
-Be SUPER efficient before you get to the boss room. There are 2 main Taken rooms you have to clear first: the big hall before the tank room, and then the tank room. The first room ain't bad, just be quick and move on. The tank room has two annoying threat types: Purple shielded major wizards and major vandals that snipe with solar attacks up top where vandals noramlly spawn during the strike. Send one hitman to wreck these up top (or snipe them) while the other two are destroying the minions. Clean up the wizards together and move on to the boss, clearing a couple more groups of minions along the way.
-At boss: Stay in the little entryway into Tanik's main room. Bubble obviously helps (use blessing, not weapons). Minions will be bombarding the fuck out of that place from both sides. -Prioritize killing the minion spawning big black orbs (a few spawn around the room) and the boss. If you ONLY focus the boss and ignore all minions and spawners, you'll probably get so overwhelmed that it will be impossible to poke out to hit the boss. So manage minions if they get too built up, and prevent the buildup a bit by killing their spawning orbs. Kill boss in bursts of damage by poking out and back into cover.
-After boss dies prioritize finishing the spawning orbs which respawned throughout the boss fight. Once dead they'll stay dead after the boss is dead. Next priority is PSIONS. The first couple times we didn't take them seriously and chased down the fatter guys: knights, centurions, and captains. Mistake! Even if you clean them up by that point the psions will have multiplied into a sea of clusterfuck. Even if they don't kill you it'll just take forever to burn them down. So have at least one guy destroying them immediately after boss dies. Others focus down the black spawning orbs, then finish the fatties.
-Timing: You know you're on a good pace if you get to the boss room at ~6 minutes. If boss dies at ~3 minutes you're on pace.
-KEY: Don't die! (DUH) Dying forces a 20 second self respawn timer, or 10 seconds if a teammate can pick you up. Being dead 10-20 seconds multiple times really hurts progress. On our first couple runs we had ~15-20 deaths between us. Last successful run we had under 10 total, so aim for that. Don't waste time!