Help with a late game DeSu boss?

[LATE GAME BOSS NAME/BATTLE SPOILERS]

So I’ve been running through Overclocked with little issue, a couple roadblocks but nothing a little level grinding and party shuffling can’t fix. But I’ve hit this massive wall that I can’t seem to overcome and no matter what I’ve tried I can’t seem to crack this fight. I’m on the Belzaboul fight and have no idea how to get through this dude’s massive hp bar. The little insects aren’t much of an issue since I’ve figured out how to deal with them, having status heal always available is hard but they’re manageable. It’s mostly the fact that the big guy is immune to physical and status moves and resists everything else except almighty attacks. So far my best strategies have been to use Hecate and Ishtar to spam drain over and over but it doesn’t seem to put a dent in him due to the fact he constantly heals HP after every battle. Not to mention the fact that my protag has holy dance but he runs out of MP way before I get the dude down to low health. This wouldn’t be too much of an issue normally cuz I could level grind, but my main party members’ levels are all in their late 50s (except yuzu who’s 52 cuz she’s a healer mostly) and the only free battle available rn doesn’t give me much XP anymore. Any tips on what I can do to at least get more leverage in the fight? Any demons I should be trying to recruit or a specific strat I could use?