you know they could probably change it so that IG only effects mobs in your LOS (line of sight)
but then a lot of the time mobs will go under the map or inside walls and still be able to attack you and your groupmates and that's one of the things that IG is really good for, for getting aggro on those mobs that you can't see or target because they are out of your LOS for whatever reason...the problem is distinguising between mobs that have already been aggroed and ones that haven't
i think the real solution to this and many other problems with this game though is just to simply make it so that no mobs are capable of going through walls at any time (except for maybe ghosts since it makes sense for them to be able to)...make them obey the same clipping laws that we are forced to follow...if they are supposed to be physical beings like us then why should they not have to follow the same laws of physics in the world that we share...that would keep mobs that you have pulled from getting stuck in walls and the ground and becoming bugged like they oftentimes do and keep mobs that you can't see on the other side of walls and stuff from aggroing you out of nowhere, whether you casted an aoe or not...i know that many of the mobs in OLS will aggro you right through the walls if they are on the other side, IG or no IG, and that is just not right...this has been a longstanding problem in many zones that they should have fixed a long time ago if you ask me
lets hope that they do sometime very soon