Alright, Omega Apex mastered in 28 seconds. I really dislike a fight designed entirely around stop, because it's just completely RNG retardation. Did stop land every cast in phase 3? You win! Did it miss a single time? Game over man, game over.
Team I used:
Bartz -- Snowspell Strike -- USB
Squall -- Blazing Twinstrike -- BSB2 (only used last turn as a finishing hit)
Entrust Battery (I used Faris, she has high speed)
Ramza -- Armor Breakdown, Fullbreak -- Shout
Yshtola -- Stop, Shellga -- BSB
RW: Cloud USB
Video:
Omega 28 seconds
So the way I did it was Bartz and Squall called in Cloud USB RW right away as their first action. My entrust battery wrathed twice then gave Bartz a soulbreak bar so he could go into his USB crazytown damage. Squall was mostly just support dps, any legend dived physical dps could replace him. Yshtola did Shellga -> BSB -> Medica -> held her turn until P3 begins, then stop every round.
I tried many times early on to tank it up and survive his damage, even a few attempts with Vaan and four healers (really), but once the boss hits phase 3, he literally does a massive aoe nuke every 0.3 seconds or so, completely impossible to survive if he's not stopped.
Key to the fight is to burst him down extremely fast to phase 3, then stoplock him and continue bursting the hell out of him so he dies before a stop misses.