As per any testing, if you remove a variable and the outcome remains the same, you've not removed the cause.
I think everyone must know that, deep down. It's absurd to think that someone could have 20 different people to do jobs and then do them for them. There's not enough hours in the day.
The issue, for me, has not been cumulative and consistent - we have had good DoFs in the past, with european-style 'head coach' hired to work under them. Then we get in someone who eventually wants to wrestle full control and wants rid of the DoF (Redknapp, Poch etc).
We had a really good academy under Redknapp, then Poch ruined it by doing weird things, and it is recovering now but there's no pathway (it seems) or something else blocking it.
We used to be really good at shifting players until Hitchen came in, and it was bad under the Conte era, but I don't feel like we have necessarily had an issue in moving players on recently though - it's pretty much always the issue of fan perception vs reality, in terms of people magically wanting us to get £20m for players that aren't worth £10m, or wanting the club to get rid of players (e.g. Ben, or Richarlison) that the club don't actually seem to want to sell, and seeing that being "bad at selling" rather than the reality of it.
We got £15m back for Emerson Royal, £20m for Skipp etc - which seems great now
At the moment it feels like 'The Greatest Hits' of all our problems coming together.