Here are some lines from a Fangraphs article, written by Jeff Sullivan, that I found on the topic. This is mostly in response to the criticism that Boone received during the 2018 playoffs.
I’ve long been someone who didn’t think about managers too much. And part of that is because strategic decisions tend to barely move the needle. Fans frequently get on a guy for how he handles a bullpen, and fans frequently get on a guy for when he calls for a bunt, or for how he builds a lineup, but it all makes such a small difference in the odds. Short of conceding a random forfeit, a manager can’t blow a game. Realistically, a manager can’t move the win expectancy more than a small handful of percentage points. Everything is ultimately up to the players. It’s the players who have to execute. It’s the players who determine the outcomes. Every single player in the majors is good. The per-inning difference between one reliever and a slightly worse one is remarkably small.
It’s true that, by and large, managers can’t affect the game all that much. Not if we’re being realistic. There’s no would-be managerial candidate out there who would constantly bunt with Aaron Judge, or bring in a backup shortstop to be the closer. Managers all make pretty similar strategic decisions. There’s not that much of an opportunity to make a difference.
https://blogs.fangraphs.com/the-sense-behind-ripping-the-manager/