Yeah on harder difficulties you pretty much need a team of your choice of Luke or Guy and then Jade/Tear/Anise just because they made enemies have much higher P. Defense than M. Defense and she's the only one with access to spells. That, and if you get the Ant Lion Man Doll for her, she becomes a nigh-unkillable juggernaut due to constantly regenerating HP and SP.
Natalia is still quite viable as well if your group needs the healing. Jade/Anise/Tear is great if you never need to heal at all, but if your group requires it, Natalia's Heal spell is amazing.
the main thing is to just never use Luke and Guy on the same team since enemies are built out of titanium for some reason on higher difficulties
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Geologists will date anything.