Efesia can cast spirits that protect the group from physical and magical attacks, can poison enemies and has access to almost all elements (except for fire). Most of her skills deal damage to all enemies. However, she's not pretty powerful compared to other characters and her ultimate attack isn't that useful during the endgame.
Hugo (Huggies) is kinda meh with mediocre attack, defenses and skills, but his final skill is extremely powerful.
I guess both can be somewhat useful, but they might be considered weak compared to Billy, Amicia or the other 3 remaining characters that can join the party.
Lucy (Ballonetta) is indeed the best healer but her attacks are limited to wind attacks with average damage.
Amicia has some really useful and powerful skills and she's the fastest character in the game. Also, I accidentally gave her a lot of HP so she's kind of a fast tank