Invasions should penalize all settlements not just one.
This would generally address the issue of people joining these missions to make sure they fail.
The main story has you attempt to unite the faction’s against corruption. This would fall in line with that.
Any community getting downgraded from invasion would realistically impact the other communities trade routes
Such as other territories having to downgrade defenses to pay for the loss of trade and revenue from the other settlements loss.
This would allow servers to fight the invasions as a full server. A failed invasion should have consequences for everyone. And if the vanguard sucks more reason for the other factions to take it over