I'm not asking to skip or autoresolve anything. The "hold the UFO for 5 turns" objective removes the need for my solution in UFO missions because you can just head for the UFO instead of going over the entire map looking for a few stray aliens, but it leaves me vaguely unsatisfied and doesn't solve anything when it comes to base defense, base assault and terror missions.
I mean, what happens to the aliens when you've held the UFO for 5 turns? Do they surrender? Do they blend in with the local population? Do they catch a ride back to their base? Do they just up and die? You can see how this leaves me somewhat puzzled. It's a nice game mechanic but doesn't feel right storywise.
There's nothing unique about the non-UFO missions that removes the problems either. I remember having this issue often in X-Com for all kinds of missions. Even during base defense there'd be this lone alien hiding out in the upper levels of the barracks or whatever, making me go over every part of the base again just to take down an alien that is really supposed to be, you know, attacking. In base assaults of my own I'd take out the aliens I'd come across, then eliminate the alien leaders, only to realize that the mission hadn't ended yet. Cue anticlimatic corridor-hunt. Terror missions are so large and with such complex maps that it's very easy for an alien to end up in a place you don't look, further emphasizing the problem.
Either every type of mission needs its own version of the "hold UFO for 5 turns" solution, or something else needs to be done to remove the burden of mopping up stragglers (which can and should be dangerous!). My suggestion keeps things interesting until the very end without feeling like an artificial solution.
This is a very real problem, and I would be careful about underestimating it. If 1/3 of my time playing ground missions is spent looking for that final alien (which is a likely estimate in my opinion), that means 1/3 of my time playing ground missions is dull. That's not a good thing in any way, shape, or form.