just to make sure we're on the same page when I say the beam I'm referring to the one on the far left closest to the spawn http://comp.tf/w/images/thumb/7/7e/Badlands_Last_Point.jpg/800px-Badlands_Last_Point.jpg
the medic stands behind it in a way so that the sniper can't shoot him from main or barrels. A demoman can be near main and spam pipes into stairs and you won't see them coming and even if they're called they're hard to dodge, while standing behind the beam you have plenty of time to dodge and go into spawn. With stickies you can go into spawn and someone can shoot it or blow it away it's not an issue
Edit: oh yeah sorry I totally misinterpreted what you were saying with that wall idea that's not a bunker at all my bad. But if you're going to just replace the beams with walls what reason were you trying to remove them for in the first place? That wouldn't make it easier to spam down sentries (which isn't a problem in the first place they're still possible to spam down)