I know a lot of people enjoy the narrative of the head coach being the most important person at the club, but the American sport model is more accurate. The talent and the talent recruiters are the most important factors at the club and the head coach third.
Pretty happy with this Slot guy, though, after looking at a few basic numbers (goal difference and xG difference have gone up nearly double whilst he's been in charge). Feeyenord might have had a massive spending spree in that time obviously but improvements like that aren't by chance. If he's happy to be hands-off with recruitment then I'm happy with him.