My static cleared this week. We went one Dragoon, two Bards, one Summoner, one Paladin, one Warrior, one Scholar, and one White Mage. We basically had three physical damage dealers. What we did was at phase 2 when the first group of soldiers and knights spawn, all the DPS focused one soldier until it's stoneskin broke and then had the Bard and Dragoon move to the knight.

For Phase 6, Dragoon (me) LB'd the Rook right away and then killed it. Moved to the phase 5 Dreadnaught and focus killed that, then did the soldier -> knight. Then we fed the spiders to the phase 6 Dreadnaught and burnt it down.

You don't need 2 magic and 2 physical to beat Turn 4 (I was doubtful at first but our static leader told us strategy). Good luck!