That's true. I conveniently did not bring up Killebrew
Jackson was more consistent while Killebrew had some massive HR and RBI years - many more than Jackson. But you are right - .256 batting average was mediocre, and if I'm going to kick Jackson out for that, I would have to remove Killebrew as well. My bias is probably that I always liked Killebrew and never liked Jackson. Kind of a 'Kirby Puckett vs Albert Belle' sort of thing.
It would be an interesting exercise to de-vote members from the HOF each year, until it was about half it's current size. I think there are many members who would get kicked out before either Jackson or Killebrew.