Got Leviathan up to 40% SB now. Between now and the time Leviathan expires, I could probably get another 9% SB out of it. Is it worth the effort, or should I just relax and focus on finishing the leveling of Leviathan to prepare for Bahamut?
I've found that Leviathan gains SB at a decent rate, so I'd just focus on leveling up for now. My Leviathan /\ is around 45% and it triggers most of its skills all the time. Do you have a character with anti-fire capsules? If you're going for a non-Grace Bahamut strategy, that might be more useful on your team in order to tank Meteor. Level 90 characters might be fine without it though. I'm not sure!
Edit: Just saw you have A'merpact which is what I used. You should be fine.