Interesting comparison here. Vlad Jr. has ZERO extra base chances vs. LHP yet is N-power. Semien has several extra base chances vs. LHP but is W-power. Seems SOM missed something here.
Vlad hit 2 over 124 pa's and Semien hit 3 in 180+ pa's vs lhp so it's a highly similar rate. I guess Strat has calculated that Semien's 3 HR chances v lhp + weak power equates to Vlad's 0 HR chances + normal power. Given their ballparks, etc.