The battle is fine, very beatable. It's no Schizo or Brynhilda but it is much tougher than some of the recent ones like Beatrix and rush before it is the easiest I've ever seen making it seem harder than it is.
Sleep Buster works like 70% of the time. It's very easy to beat the fight with a little sleep luck as the bosses present little threat to you, however if they wake up and a mitigation wears off they can one shot someone and ruin your perfect run (grr) - most of their abilities do shit for damage other than their 1 rare OP move. The problem I had was not enough DPS abilities causing the last boss to drag on and lose me 4 medals, I'm wondering if I should swap Mental/Power Breakdown for some Double Hits or keep them and try Advance instead for my second attempt.
Tip: Use all of your Forbidden Treasures Tablets on Phase 1 and Phase 5 for all of the eggs (10 tablets). Eggs don't take up inventory space and are ALWAYS useful. You get 2 more tablets when a new phase starts so use those 8 on the gil and upgrade mats as you need.
Also I'm finding Selphie to be a surprise super useful character. She has White Mage 4 and Black Mage 3 with balanced caster stats and the ability to equip rods, staves and whips. This means that she can be a dedicated White Mage or a Black Mage with Shellga/Protectaga meaning no more 2 White Mage required teams for maximum mitigation.