I only got Rydia to 99 (and with all stats except HP maxed out, and I gave her the HP+50% augment to allow her to reach 9999HP as well) in a DESPERATE attempt to solo Proto-Babil. Too bad, I found out that since Rydia can do around 22,000 damage at most with double-casted meteor (after using Cry to lower defense) and Proto-Babil can heal for 24,000+ when he gets below 120,000 HP AND at that point he starts to counter with a fixed 9999 damage attack, it's actually impossible. Sad but true. I managed to solo everything else at lower levels though.