I know the Arcs are somewhat the size of a reaper .... 2km in length and the Nexus is 4 or 5 km in length?.
And we can assume that there is going to be a native race that is hostile towards us.
Do you think the Arcs will be armed to the teeth? They seem to me like nothing more than big transports with a huge engine and a docking station, same goes for the Nexus. Maybe some GARDIAN lasers, but they are just Anti Fighter/Bomber, Anti Missle Defence Systems.
I haven't seen any Battleships in any of the Vids, no Cruisers, no Frigates. The Tempest is almost unarmed, the Nomad aswell.
So how do we defend ourselfs except for small arms and biotics?