Well, I'd recommend switching Teddie for Yukiko. As I said, Yukiko is widely considered the best party member, and Teddie the worst. They both fill the same role in battles, but Yukiko has better magic and skills. Chie and Kanji fill the same physical attacker role in battle, too. Chie is better with random encounters because her physical skills attack multiple targets, while Kanji is better for bosses because his skills attack one enemy and he has a higher strength stat.
...What? Since when?!? Teddie is arguably the most versatile party member in the game after the protagonist. He is the undisputed best source for buffs after the protagonist. He is the second best healer in the game and his good magic stat makes him a good backup attacker.
The argument that he's made redundant by Yukiko is completely absurd. The 2 characters work very well together; not only does Teddie resist her weakness, and his access to healing takes the pressure off Yukiko (IE, you run into situations where healing is needed and Yukiko's has already been used) but he is capable of focusing on his buffs due to Yukiko's access to healing. Teddie is a
very solid character.
Seks, just run with Yosuke, Kanji and Teddie. Mind Charge / Agidyne spam with protag, Yosuke is on support (items, backup offense, etc), Kanji should spam Fatal End (I don't know why you were using Zionga, Kanji is a physical attacker) and heal with Teddie when needed. Grinding won't get you any stronger; you need to overcome Mitsuo with strategy.
PS: Don't bother with Yukiko now. She learns Mediarama at level 43, so it's simply out of your reach for now. Have her catch up in the next dungeon. You definitely fucked up when you dropped her for Kanji. Kanji/Chie is a redundant combination, you should have focused on one of them.