That K rate is inflated from facing worse competition, and the pitcher spot 3 times a game.
Would you agree a pitcher is more likely to strike out than a DH.
Strikeouts also a key driver of FIP XFIP numbers
NL FIPS and XFIPS are Inaccurate for this reason alone.
Look at the DHs in the AL, Ortiz, EE, Victor Martinez
The DH is usually one of the best hitters in the lineup. in the NL They face the pitcher who is unarguably the worst hitter in the lineup
How many times during that year did he strikeout the opposite teams pitcher that year? replace that in his K Rate with the average K rate of the DH in the AL that year, and you will surely lead to the same K Rate in his AL Days.
Not to mention that in most NL teams, the 8th hitter is usually also a terrible hitter.