Okay I have Storming the Spire sussed out. The side facing the starting point is the "hard side" or front side, and the other side of the spire is the "easy side" or rear side.
The front side's task is hard. They have to defend our troop transports from being destroyed before they can unload troops. So they have to take out *everything*, including Voth ships, swarmers, turrets. And in phase 2, they have to take out the Voth Dreadnaught ship.
The rear side's task is much simpler, prevent Voth Troop Transports from landing and unloading troops. So the easy side's task is to take out Voth Troop Transports. The other ships are pretty much optional. And in phase 2, all they have to do is take out escaping Voth shuttles that blow up easily.
Because of this, I think the best strategy is to assign 3 of the best, highest damaging ships on the front side and have the two weakest ships to the rear. So there are 5 players and 5 defensive positions to fill, Front Left, Front Middle, Front Right, Rear Left and Rear Right.