No, you didn't. Seriously, my first win, we had 2 dps on cannons the whole damn fight, me (Monk) and a dragoon, one of us with Zeta and the better geared of the lot. The cannons and dragon killers landing every single hit on vishaps feet will do well over 70% of the damage needed, the rest coming in from short bursts between each gate and the LB 3 you should have nearer the end.
Even perfectly executed, that's still a huge chunk of damage you have to do without mechanics, so I fail to see how you're refuting my point.

As for "one shot mechanics" none exist. Stand under his feet and you will die if under so much HP, but what the hell do you expect.
Body Slam = 1 shot to non-tanks
Sidewise Swipe = even if you dodge this, you can still get 1 shot by an exploding cannon
someone shoots 2nd/3rd dragonkiller at wrong time = whoops, you just killed your party

Uhh, yeah, there are 1 shot mechanics here.