You know, this reminds me of my attempt to play original Final Fantasy and get everyone advanced by level 10. This means rushing to the city in the crescent lake to get the canoe (which means beating Litch), then going through the Ice Cave for the aircraft, then going through the Castle of Challenges for the Rat's Tail. By level 10. Both the Ice Cave and the Castle of Challenges are rediculously hard. Plus, the Castle of Challenges, you have to get both to and from it from the only landing place on the land mass it is on. Although at least tents help there.

You just have to Play Smart(tm). You had a good idea with Cuthulu Defending, the Taunt ability he picked up several episodes back did a good job of keeping the casters alive, particularly October so she could get her Fire Storm off, which is really only useful if it gets two or more shots off (otherwise Fireball/Tempest is more cost efficient).

Sharpe would have likely also done well as a 'party tank', with his self-heal and buff ability that he has. IIRC, he's also got Taunt with Defend. Then you have Cuthulu Dark Strike when you get a Dragon, Umi Flood and October Flame Storm/Tempest.