I slayed monsters until I was max level and then just used Lyric to keep up the healing over time on everybody. I struggled a lot before but with that it was surprisingly easy, but I absolutely get what you mean, was stuck there for some time.

Actually every single JRPG is about to grind levels. JRPG games are tend to be mathematically correct at some points, given a little rng into the system. If you want to beat them, then go and level up your characters, this is always the key in every single jrpg game. The difficulty is just right. What the point of playing a game if you are always winning.

Fighting even under-leveled (within reason) isn’t that tough if you focus on draining his mana first. As long as you’ve got good defensive equipment on the squishies to prevent one-shotting and apply regen you won’t even need to use much in the way of items.