You're old fashioned
WAR agrees that Yelich has been the better hitter this year, even with the position adjustment. According to baseball ref, Yelich worth 2.1 and DeJong 1.8 on hitting alone.
DeJong's 167 OPS+ year to date pretty impressive for a middle infielder, but Yelich has a 223 OPS+
The difference is defense --DeJong 0.6 WAR and Yelich 0.0.
Of course WAR doesn't predict future performance. Yelich is still almost certain to end up with a higher WAR for the year than DeJong.