I tend to support the manager and coaching staff when the team underperforms. These guys know basebal land they know what helps being a winning baseball team. The manager puts out lineups to reward players that deserve at-bats. Coaches, as a group, work to make their players better and most of it is on the players.
The cost of hitting for relative plus power has been so many strikeouts. The continued inability to get big hits is a virus for the entire team, but especially for the few "proven" players--Buxton, Correa and Vázquez, who also are the three players with contracts through this year and two more years--all have dreadful clutch stats. Kepler shouldn't be a starting outfielder with his hitting stats and Gallo an accentuation of what is wrong with the slugging-heavy hitting approach. The team has played much better when Polanco is in the lineup.
Perkins said on the broadcast today that they should improve by regression to the mean, which makes sense, but there have been too many just plain awful plate appearances. If any of the management staff is in trouble, I would imagine it would be the hitting coach(es). With Kepler and Gallo being in the final year of their contracts, I could see one of them being shown the door. I do have confidence that Buxton can be an asset even as a full-time DH, but the long periods of empty at-bats shouldn't be happening with a guy with his skills.