I absolutely DESTROYED T-Rex this time. Got 8/9/9/7 on the 4 levels. The key thing I improved upon over my previous failed runs was:
1) Created a second double cut and honed it up to 6 uses.
2) Honed Blizzard Strike, Blizzara, and Blizzaga each one more time.
3) Used Cura and double cut on the Forbidden trash mobs to kill them more easily
4) Poisoned the boss.
I couldn't get blind to land, even with Dark Buster. By the time I got to the boss I had about 6 total uses of blizzard/blizzara strike, 8 combined uses of blizzara/blizzaga, and 8 curagas.
Wakka had 2 Status Reels ready to go, so I'd get a Status Reels off and then just unload with all the stuff I had. I took some damage from his counter attacks since I didn't manage to blind him (that was the only place I lost stars), but Aerith's Seal Evil stopped and silenced him a few times, which spared me some of his worst AoEs.
Overall I think he went down in less than 10 rounds, I was doing anywhere from 10k - 15k per round raining blizzaga, blizzara strike, and double cuts on his face.