Why did we expect a B?
His last 3 seasons with Detroit.
His final grade was a B- or C+.
He was a B from 2016-2018. An F or D in Ben & DD's final seasons.
I don't think it's sugar coating to discount a pitchers first 3 seasons, especially at ages 20-22, when you have 3 full seasons of sample size from ages 23-25.
There is no doubt, his 2015 season was an outlier, in this context. When you count what he did in his 3 years afterwards, it is even clearer.
Ages:
23-25 good (4.08)
26 bad (4.92)
27-29 good (3.99)
You can call it cherry-picking, but those are the meat of most any pitcher's career, and it is usual to expect a bell curve and not a low spike right at the peak of prime.