They could have made this less of an issue if Kerrigan was actually hunted in some of the missions. In WoL, Kerrigan was force targeted by most of your army, and you never see that kind of AI response in the game. I expected to see ravens with seeker missiles wiping out all the lings, advancing siege tanks, thor drops to cut off escapes, and a bunch of stimmed marauders running up to a lone Kerrigan unit caught in the middle of a map suddenly with no backup. Maybe a few teams of airdropped merc marines for good measure. You know, the kind of desperation kill that every player was forced to do in WoL.
That Kerrigan needs the swarm to survive and everyone wants her dead is never really fleshed out in the gameplay either. I expected Kerrigan to be a powerful unit that you really had to fight to keep alive and using. Instead, many of the missions ended up having Kerrigan as a base breaker and the other units at meat shields. There's never that sense of 'oh crap, I'm all alone in the open' that there should be. Even micro'ing out in the open with a lone hero unit in Marine Arena captures that feeling better than the campaign missions.