Granted, they added JD Martinez, so that's helped, but Boston 2017 to Boston 2018 would show that a hitting coach does matter that much. He was there in 2016 too though, and they were better that year than this year in literally everything (HRs, slash line, wOBA, wRC+, etc) I have no idea what it is. Would the presence of David Ortiz in '16 account for that difference?