[emphasis mine]
Yeah, limit -> not make outright impossible.
This.
The problem with the skycade is that you are building into a nodraw area. An area of the map which was never intended to be at, you are using an invisible wall to place the cade kit, then boxing it off as best as you can to prevent entry.
If you had done this, say, on the ledge of the roof, not a problem.
But when you climb up to the edge of the playable ceiling built into the map, then we have problems.