The issue with Walsh was that he was a good head of recruitment/Scouting but completely out of his depth as a DOF. At Leicester I understand he was an "Assistant manager" which is obviously a very different skill base to being a DOF.
One thing I don't doubt is his ability to spot players. Even with us players such as Lookman, Vlasic, Onyekuru, Gueye etc. He also looked closely at D Gray, Leon Bailey, Isak, David Brooks, both the Sessegnon twins, George Hirst etc. There were obviously a few flops too, Gabbiadini he liked has struggled, a CB at City he wanted has likewise, Belfodil hasn't been up to much. However in general his eye was good and the players we could have bought would have worked a lot better for us than what we ended up doing.
The first major issue he had was he really struggled to close deals, the 2nd being that he worked for a manager who had a radically different approach to what he wanted. He was signing often younger, less well known players, yet we had a manager who was obsessing over PL experience. It didn't take a genius to work out the two things were at opposite ends. You throw in a completely inefficient board who aren't capable of managing a successful PL club, who just let these problems slide and it all came crashing down.
While he's probably right re Maguire, Robertson and Haaland, in truth had they been signed, under Koeman none would have flourished.