I going to go out on a tenuous limb and say this is probably on purpose. Not everyone is great at combat, and not everyone enjoys it. I think tricks like these are left in for people who are tenacious enough to try everything to get around an encounter.
There is a comparable exploit for the goblin ruins as well. After fighting the Githyanki at the bridge, I jumped across the small divide which leads to the back entrance of the goblin camp. With cantrips and arrows I took out the Ogre and twenty or so goblins from heights they had no pathfinding to reach, eventually went through the broken passage to the top of Priestess Gut's sanctum, then followed rafters and ledges all the way around killing 90% of them without them even knowing they were in combat before dying. I tend to like Splinter Cell opportunities like this and while I am sure I missed out on a ton of cut scenes with all of the named enemies I am not too bitter since I wasn't going to let anyone of them live anyway.