It doesn't hurt that Ken has seemingly unlimited cash to foster his car bug. If I had his resources I'd be doing the same thing whether I was a good driver or not. He's out there having a hell of a lot of fun which is the name of the game!!! But in reality, Tanner Foust is a better driver and far more personable AND he drives pretty much an identically prepared Fiesta as well.
Note: while both Ken's and Tanner's cars are capable of 650+HP they rarely operate them at these levels (the motors are time bombs at those boost levels). For U.S. Rally both cars are tuned to under 400HP for more controllable wheel spin (read tire life). And for WRC competition (where Ken dabbles around) they aren't allowed to have more than 300HP.