Of course, there are flaws in the players on the team. I don't think Onana is the only one to blame. Erik ten Hag, who cannot read the game and make the necessary moves, is one of the culprits. If there is still no success despite huge transfer budgets, I attribute this to the wrong player transfers and the coach.
Anyone who work in Manchester United has it's own mistake, resulting the poor performance in Manchester United. It's the time for Manchester United to sign a coach from top team, they've tried to sign top players, but all of them mostly flop when they play in Manchester United.
There are only three coaches: Pep, Ancelotti or Klopp.
In a club, the one who is fully responsible is the coach because he alone sets the strategy including which players should appear on the field even though we see Onana often make mistakes but when Erik Ten Hag believes in his goalkeeper now then it will not change much to change because he believes too much.
We see that Manchester United have recruited many talented players but they are still difficult to advance their team often losing and difficult to win, Erik Ten Hag's philosophy is still not convincing even though some believe that someday he will succeed with his team now.
Is that the most successful coach? Yes I see these three coaches are on a good path right now.