Like I have said previously, mage isn't the only class that bring BL/Hero. After, Like I have said before too, if the mage could have done 5% more DPS, I could have say OK there needed to beat the enrage timer.
But it's not the case.
On a second hand, we have a number of guild, from top world to normal progress, that exchange mage for warlock (or a 2nd one) on fight like Qwon HM and Animus HM.
It's not foolish, it just they can without losing any thing add the little utility that can help a lot for downing the boss.
Why the mage ?
because it's the class the most easy to replace. Mage aren't hybrid, it don't have any useful spell that can help on this fight.
I don't say they don't have useful spell.
But there's certainly other class that are also in the balance on other fight.