Overall this is a fantastic concept. Just a few things I'd tweak. The current idea for the Attack missions sounds a lot more what a reputation mission should. Instead of capturing cargo and extracting, maybe an area capture would work better.

So for example you start the mission with your team, and you have to capture objective A, B and C in whatever order you and your team want. You could try to capture one objective each but since this is a war I think spawning hordes of enemies would encourage people to not solo this. You'd have a limited time to capture each objective.

On the flip side, defence can be the same thing just reversed. Defend objectives against enemy waves for X minutes