Just finished this, took me 12 hours from lvl 75 using Sendai Dire Shadow. My strat was Wolf for Debilitate and Heat riser on everyone, then Joker with Futaba Charm and Lucifer spamming Blazing Hell, then using Ann and Sophie when Joker ran out of SP. Lucifer also had every stat maxed so I would switch to Joker for All-Out Attacks. Each fight takes about twice as long as Metatron (on Easy), but gives 4x exp so it ends up being way faster. Also a lot less boring.