Griemdaall,
The exp gained at the finish of the mission is miniscule compared to killing a couple mobs in the mission. This coupled with the fact that team missions do not work at all means no this is not an exploit it is just a very small amount of experience a small bonus if you will to completing the mission.
If team missions worked then people would be doing those instead of solo missions in a team. Team missions have never worked and I have to wonder just why they don't seem to want to be bothered to fix them. Right now teams doing solo missions is the only option as a team mission so it is not an exploit as it is the only choice by FC's own actions or in this case inactions to fix a problem that has existed since beta like so many persistant problems in this game. Once again as usual they chose nerf rather than address the real problem.
They need to eliminate the team mission kiosk completly replace it with another mission kiosk like the solo one leave things as they are and wala no coding to nerf solo missions and they are let off the hook for fixing team missions. An easy slick and intelligent solution.