Well, if IP's don't count, Buchholz was our best starter in the John Henry era with his 16 starts and 1.74 ERA in 2013.
As for Sale, I think he's the most professional pitcher I've seen in a Sox uniform, but the fact remains he stunk in the 2017 postseason, pitched a short 2018 season (27 starts, but a terrific 2.11 ERA), and had no quality starts in 3 postseason starts in 2018. Price, Eovaldi, and even Porcello all had better ERA's in the 2018 postseason.
Pedro was definitely an ace in 2003, first year of the JH era.