We're barred from server first Turn 4 because..

[Inosaska]

The first time we cleared turn 4 was with a warrior. The PLD was tanking the two dreadnoughts and the warrior tanked the adds in the back.

I think you missed the point of the post as it cannot be done with a main warrior tank and requires a PLD to tank the dreadnaughts. Get to turn 5 then you will see why everyone brings double PLD for the fight.