Warsong can give the reroll to your flanking calvery which is where I see the gain from that section of the upgrade.
As for the large block, I would actually consider supporting it with two blocks of 2x2 archers equipped with dispatch runner/rally/Sim to give your giant block three attacks. Combined with warsong that's going to be a lot concentrated fire. Doesn't necessarily help with survivability, but it does get the damage in fast.
(Also dispatch triggers a melee attack so you don't want to use it on archers)



