This is the entire problem they bought players with no regard for how they would fit a system.
Firstly, you need a system first for them to actually fit into, which we seem totally void of. It's like they picked names and then work around them.
The early days of players pressing has gone by the way side, probably because we don't have the players for it, and width is non-existent.
So Koeman needs to pick a system, choose players who suit these roles and equally instil some tactical discipline so they don't amble around.
People say Gylfi and Rooney shouldn't play together - maybe so; if they are however, then Koeman needs to tell them to play like professionals.
Instead, they ramble around like children on the playground with no tactical discipline and then we wonder why there's so many gaps.
Anyway back to Walsh - regardless of Koeman's influence, as DoF then a poor transfer window must be to some extent his responsibility.