This isn't an exploit, but it's something that I could see Blizzard adjusting with just a small tweak; Make him throw up his 99% shield at 70% regardless of what he is doing at the moment.
But exploit? Not really. The fight just has a lenient enrage timer, and low raid damage in p1 if you're slaughtering all the oozes and eating a puddle here and there. This allows people to durdle for 8 minutes :P
Well, even if you did that, you still had to deal with some portion of Phase 3, just not as long, but still enough to cause issues if you didn't attempt to respect the raid damage/constructs. Shortening one phase is different than skipping TWO phases which span 5-6 minutes combined.