The "Kill Arken" mission is not typical of something a team would ordinarily do on the mainland (in terms of most team members trying to get credit for the killing).
I suspect that the granting of just one mission completion per team for the killing of Arken was done mainly for the sake of keeping the programming simple. The granting of one mission completion at a time is a tedious pain for the players, but granting of mission completions to all team members for one killing would be too easily exploited. Anything in-between would involve to much programming. So what we have is less than ideal, but at least it exists and has a good reward! :)
Perhaps the best situation would be for seasoned characters to team up to help newbs complete the mission...
I suspect that the granting of just one mission completion per team for the killing of Arken was done mainly for the sake of keeping the programming simple. The granting of one mission completion at a time is a tedious pain for the players, but granting of mission completions to all team members for one killing would be too easily exploited. Anything in-between would involve to much programming. So what we have is less than ideal, but at least it exists and has a good reward! :)
Perhaps the best situation would be for seasoned characters to team up to help newbs complete the mission...