Foundry is a lot of fun and I have played some great missions. However, except for VA's who don't need the xp it's hard for lower levels since they get no xp. However, I also recognize that givng xp for mission can be exploited. However, I had an idea. Give 5 xp for each objective. Objective would be inteactions, talkng to contacts, or killing enemies. Each enemy group would count as an objective. This can lead to some decent xp and remove any exploit. If you want to create a mission to to kill a 500 ensign groups to get 2500 xp then so be it. It's still gonna take a long time to kill 500 groups.
Can this still be exploited? Yes, but it makes it much harder.