two things...

[aerialrave]

Tank LB can help but it's by no means required to win this fight.

If you're taking too much damage from her ultimate ability, it means too much of the rocks were destroyed.
If too much of the rocks were destroyed, that means either your DPS didn't kill the plumes fast enough, or you positioned the boss wrong and Garuda smashed the rocks herself.
It is actually a fight mechanic that the rocks defend you from that ultimate ability, and the plumes break them down for the first half of the fight. The more rocks that are left standing at that point, the less damage you take.

Positioning is key in this fight. If you got her outside facing perfectly, there isn't much you can do outside of captaining the team and directing them to kill the plumes ASAP. As a tank you cannot attack the plumes without Garuda following you. There isn't really anyway to do it because Paladins don't get Circle of Scorn until Level 50 and even if you made it that far you are sync'ed down for this fight. If you are REALLY desperate you could try Flashing the Plumes right when they come out of Garuda and hopefully they will get blinded causing them to miss their attacks on the rocks for ~12 seconds. Also if you are lucky you can toss a few Shield Lobs to the plumes that are nearby. For the ones in the back, you are completely relying on your DPS to get the job done.

I am sorry that you have been stuck on this fight for so long. Most people are able to complete it in a day or two. I am also very surprised you are getting long queue times as a tank.

[Sagittarian]

If too much of the rocks were destroyed, that means either your DPS didn't kill the plumes fast enough, or you positioned the boss wrong and Garuda smashed the rocks herself.

Or dps/healer were standing too close to the rocks and let them get hit with her aoe. That's the most common error I see.

As a tank you cannot attack the plumes without Garuda following you. There isn't really anyway to do it because Paladins don't get Circle of Scorn until Level 50 ...

She's a warrior. So just overpower.

The only other thing I can suggest is upgrade your body armor. Try for the Sentinel's Cuirass from Dzemael Darkhold. Otherwise get High Mythril Armor.
If you are still struggling then fate/leve grind to 45 and do the warrior quest. That will give you several new pieces of armor.

Zodiark is in the Chaos datacenter so you will get faster queues if you are playing during prime EU time and select multiple languages (if you are comfortable with that). You can also post in the Zodiark section of the forums, put up a party finder in game for help, or ask your free company.