Well you've missed the point again. Of course recruitment and the squad are the main problem, but managers have still failed too. More than one thing can go wrong at the same time, and we are clear example of that. Almost everything has gone wrong at the same time which is why we are in such a bad position.
Martinez was sacked because of the worst home record on record and taking a 5th place team to 11th twice.
Koeman was sacked for spending an absolute fortune and leaving us in the bottom 3
Allardyce was clearly hired as an interim - rightly or wrongly.
Silva was sacked because he left us in the bottom 3
Ancelotti left of his own free will to join Real Madrid
Benitez was sacked because of the worst run of form in our PL history with 6 points from 13 games.
If we leave out Allardyce because he was an interim (IMO) and Ancelotti because he was not sacked, then can we really argue any of the other 4 were good enough? I find it very hard to argue they did well, regardless of the recruitment. And these managers were involved in a lot of the recruitment too, so again take some responsibility.