Sox SP's averaged exactly 5 innings pitched per start last season (21st in the league). In 2021? The averaged 5 IP (18th in the league). Back in 2018, they averaged 5 1/3 (17th in the league).
It really hasn't changed much since Cora came onboard. While starters are throwing a little less, it's in line with the trend across MLB. At least now, there's an extra reliever you can put innings on as the rosters have expanded.