Of course none of us will ever know the innermost workings of our club but every indicator of the information we do have access to points to Koeman shouldering little if any of the blame. I wonder if you'd be as vehement in your critique of those "absolving" him if we hadn't just rolled over at Chelsea. It seems like a flimsy stick to beat the manager with.
Also thanks for ignoring the part where you confidently claim no manager is ever involved with negotiations. That's part of the reason for directors of football, spread out the temptations and less managers will be corrupted by the brown envelopes they get offered.