Indeed the Red Sox last year scored 101 more runs than they closest American League rival, the Cleveland Guardians (who this offseason added Edwin Encarnacion while the Sox lost David Ortiz).
The previous year the Blue Jays scored 127 more runs than their closest American League rival, the New York Yankees. Without losing a David Ortiz-caliber hitter, the Blue Jays in 2016 fell to fifth in the league in scoring.
In 2016 the Red Sox received stellar performances from Mookie Betts, Dustin Pedroia, Xander Bogaerts and Jackie Bradley, who posted fWAR pf 7.8, 5.2, 4.8 and 4.7, respectively. These are four great players but I doubt more than one will match or exceed his 2016 fWAR (and the current Steamer, ZiPS and FanGraphs Depth Charts projections support that). Few Red Sox players are projected to regress upward.
The Red Sox deserve to be in the conversation of American League favorites but I'm unconvinced that the Sox have made a net improvement over the 2016 AL East champs.