Crochet has been as good as advertised, but Chapman has been better than anyone expected.
Crochet leads the AL in games started, innings pitched and strikeouts: 2.26 ERA, 1.032 WHIP, 11.2 K9.
Chapman has pitched in twice as many games but in 30% of the innings: 1.13 ERA, 0.794 WHIP, 13.2 K9.
Crochet: 18 games started. Chapman: 21 games finished.
The question is: who has been more valuable? WAR assigns numbers for performance, but there are no stats for positive effects like conserving the bullpen, setting examples, eating innings, providing confidence and inspiring teammates in the dugout, clubhouse, hotels, planes and busses.
Both are the best Red Sox players at their positions. Like WAR, I have to give a slight edge to the guy who pitched more innings and retired more batters... so far.