WAR isn't perfect. Maybe you saw bWAR in this time, but Buehler's 2 year average fWAR is 4.05, and Kershaw's 3 year average is 3.67. (2 year = 3.35)
I don't know how bWAR underrated Buehler's 2019 season, but I cannot agree with 182.1 IP 3.26 ERA 215 K becomes 2.2 bWAR.