I'm probably the world's leading advocate for this year's Sox rotation, but even I have to agree some regression is possible/likely.
However, I also think right now, 49 games into this season, this is the best Sox rotation in a long time--measured by the fact that the team ERA, 2.95, is just behind the Yankees' 2.92 for the best team ERA in MLB.
The 2007 Sox team ERA of 3.87 was 2d best to the Padres 3.70--for an entire season of 162 games. It was even better, 3.29, in the 11-3 postseason when the Sox beat the Angels, Guardians/Guardians, and Rockies. Back then starters were bargains: Schilling $13M; Beckett (the ace in 2007) $6M; Matsuzaka $6.33M; Wakefield $4M; and Lester $384K.
Flash forward to genius CBO David Dombrowski's 2019 Sox rotation, the one that couldn't even make it to the postseason: Price $31M; Sale $15M; Eovaldi $17M; Porcello $21M; ERod $4.3M. The 2019 Sox team ERA was 4.70 and ranked 19th in MLB.
Now contrast the 2007 Sox, who won the WS by sweeping the Rockies, with the 2019 Sox, who didn't make the postseason--and you have some idea of why JH fired genius DD.