Im currently using kanji, naoto and teddie and all 5 of them (including pro tag and rise) is currently level 82, the protags persona is Mada at level 83. For equiment everyone has +300 damage items and for armor everyone has armor that gives +200 defense. I curently have 40 antibiotic gel and 35 macca leaf.
Now then before anyone says anything all of the other characters are horribly under farmed (yosuke, chie and yukkio are all in the 40-50s range).
I see, I see...
Well Naoto is ill-advised for the final boss because her damage is terrible (she excels in random battles). Unfortunately, Yosuke, Chie and Yukiko are beyond help (unless you want to waste an hour grinding on golden hands) but the boss battle should still be doable without them.
Here's what you want to do:
Pre boss battle preparation
Fuse
Trumpeter, a powerful Judgement Persona. Trumpeter comes with the Debilitate skill, which lowers the targets Attack, Defense and Accuracy/Evasion. Since your Judgement slink is effectively maxed, you should be one level away from obtaining this skill. Grind until you obtain it.
Boss Battle Strategy
1. Teddie is on stat buff duty. He should work to set up Matarukaja and Marakukaja and maintain them for the entire of the fight. If they're set up, he should be on healing duty.
2. During the fight, Kanji should be alternating between Power Charge and Primal Charge for heavy damage. His endurance is high, so he shouldn't be taking much damage.
3. Naoto should be the secondary healer/buff user. Her damage is pitiful so there's little point to attacking. Focusing on ensuring that everyone stays alive
4. The protagonist should use Debilitate immediately and attack with his strongest Persona. Make sure it sticks on the boss, or else you'll eat big damage.
Remember, if the boss has used power/mind charge, be sure to set everyone on block. You can't afford to take unnecessary damage. Keeping everyone alive is the key to victory, because it'll hard to mount a comeback if you're down to 1-2 party members.
You should be able to win if you follow this strategy to the letter.