Well, I have to disagree with you. Chris Armas was a disaster, playing people out of position, wedded to his "idea" despite a roster completely unsuitable for it. Nearly destroyed the club. On the other hand, look at the resurgence of Nottingham Forest under Steve Cooper.
Coaching matters.
As for Chelsea, sure, it had the infinite resources of Putin's buddy seeking to sportswash his money and reputation. Hardly a model for the rest of soccer.