Well, yes, but there's nothing wrong with a meatshield. It's a pretty neat trick, and I think it's very far from overpowered (what are the chances that something in between you and a powerful monster is actually immune to something the powerful monster isn't?). Now, certainly for things like orb guardians, this might be a little cheap, and maybe it could be improved there--I'm not entirely sure. I do think that for most things, there's nothing wrong with the old behavior, whether people think it "makes sense" or not (which I find a pretty lame rationale overall). When you concentrate on things like titans, greater molochs, and orb guardians, you start to miss the bigger picture.
I very much disagree that this stops the nuisance of summoners--in fact, I find it very much exacerbates it. While summoners do have a change of switching in, unless you manage to kill it, it could very well be gone the next round--to the complete other side of the room!. I've had this happen, consistently, with all sorts of summoners, even going into berserk--jackalweres, werewolves, dark elven wizards, DE priestesses..the list does not end.