Disagree. He's judged on the performance of the team. Period. He doesn't buy anyone. If Walsh can't get him adequate talent to replace Lukaku and whoever else, that's not on Koeman. Now, if Koeman told him buy Pickford, Keane, Klassen, and Walsh agreed and bought them, then yes, that's on Koeman if he can't get them playing at a high level. I'm sure Koeman is telling Walsh what he needs and Walsh is trying to satisfy those needs (as well as plan for the future and many other duties).
Now I think it's fairly obvious who Koeman and Walsh have gone after. If we get another 3-4 in and they are a combination of the players we've been hearing about, then yeah, I'd say much of it is on Koeman.