repeating a mission for the same amount of skill points is something that will get nerfed in the future. Cryptic has stated that repeating a mission offers diminishing returns. So the benefit of double xp for a single mission is not intended.
It is less than ideal for those of us who want to complete the mission and move on to other things. Sure, it would be ideal if you could loop around in a mission that took only 2 minutes to complete, but those are far and few between.
And to my knowledge the skill points you get are miniscule in comparison to actually completing the episode... so why kill a few gorn over and over for small returns when you could just complete the mission faster and get a much larger skill point return? That to me, does not seem ideal.
You don't get mission xp for killing the mission mobs, though. You can't complete the mission more than once, just kill npcs more than once. You could accomplish the same thing by repeatedly doing fleet actions without taking the actual mission for it.