Tips on Minstrel Song Endgame prep?

So its my first playthrough and I'm now at the last ER (22?) Throughout the story I've been fine with finishing bosses and quests. Now I'm doing some of the endgame quests and getting wiped pretty easily (e.g. all the dragon bosses and their AoE attacks).

I've tried to do things like put up a Spirit Barrier turn 1 etc. I'll survive for a few turns but the party is always on the backfoot and end up dying to attrition.

To prep for the endgame is it just grinding a bit to get my stats up? Money has never been free flowing so I'm not sure I can just kit out all the characters with the best gear. Any tips would be appreciated.