As always - a logical argument, but I'm not sure I reach quite the same conclusion. The team's defensive vulnerability - particularly to set pieces - could be seen by a child. I'm not sure I have seen any comments demonstrating his acknowledgment that we do not utilise our offensive set pieces properly. We sure as hell don't seem to train for them!
AW may be looking to bring in players to try to solve the issue, but he's been trying that for 4 years and it hasn't worked. Look how many CB's he's been through (in itself not a good sign in the position where stability is needed most). I think your suggested solution almost justifies my question - because I am far from convinced that its an issue of personnel. I believe it to be an issue of having a proper defensive coach, and playing more effectively as a team when it comes to defend.
So I think my question still stands..