Basically this encounter has most of the primal mechanics, with a few things thrown in.
First and foremost is a debuff that the Boss will place on the tank. When it get's to 5 stack it will instant gib the tank, the debuff last about 60 seconds and you have plenty of time to swap usually we swap around 2-3 stacks.
Upon engaging the boss, his first primal summon will be Garuda which will sweep a 170 degree angle Slipstream. After that he will deal a Ifrit outer ring plume followed by a Titan Weight of the Earth inner plume, basically just dodge them. Continuing down the fight he will then summon Garuda again and summon the Vortex thingy which you should just move slightly into the middle then back out again. Proceeding from that he will do a 4 corner Ifrit Plume that moves counter-clockwise before proceeding to do Weight of the Earth on the outer field, do note that there is a small gap for tanks to stand.
During the course of the encounter he will summon a few Void balls which a linked in pairs, should any of the Void balls meet each other it will explode and deal very devastating damage about 6.7k unmitigated damage. There are 3 of these happening, first would be 2 Void Ball pairs, second would be 4 pairs forming a #, and lastly 8 pairs forming a very short 8 yard between each. First and 2nd one shouldn't be a problem, all you need to do is get 3-4 people to touch one of the linked pair. For the last one though I'd advise you to use Tank LB to take it, even in the even should you wipe and left with 2 tanks and 1 Healer/Bard you will be close to a LB 3 meter to do the mass raise.
Also during the encounter there is like a nuclear tactical launch, threatening it may be it doesn't really do much damage just don't stand near the mini circle impact point. And there will be 2 phases of Laser bots, just like the one in Temple of Qarn last boss, dodge the lasers kill the bots. First spawn will happen to have i think around 8 in the middle. You could Mage LB it but I'd advise saving that LB. And the latter is about 10 at the outer circle of the field.
Good luck in your attempt in killing Ultima Weapon Extreme. Took my group about 5 tries to observe and got it down. We had a PuG scholar.
If I have the free time I will proceed to refine this guide. This is just a rough sketch. I'm attempting other EM modes as of now...
#Thinks to add in (When I have the time)
Landslide esque Laser.
The super laser hit on tank
Tank purge
Aetherial some bullshit explosion.