I agree. This is a very frustrating issue. Almost as frustrating as having your vault member run around the room the entire combat when they have your most powerful weapon.
I agree 100%. The dwellers should be able to auto heal if you have stim packs. Say at 10% health they try and use one.
I wouldn't be surprised at all if this was by design. After all, they don't want to make things too easy on us!