The outfield defense was terrible in 2018. That was likely part of the thinking in dismissing Lieper.
Not disagreeing but wouldn't his main function be positioning the outfielders?
Pillar did not have as good a year. Could it be caused by Lieper doing a worse job at positioning than previous years?
Teoscar just cannot catch the ball. Positioning?
Can't comment on Grichuk.
The other thing an outfielder needs to do is know when to throw home or to a cutoff man? And I think that that is a basic drill taught since Little League, just like a pitcher covering 1st base. It is a reinforcing drill, not something that needs to be taught to a major leaguer.
Maybe Lieper is indeed a lousy coach, or maybe there are personality issues, but I think it is mainly a matter of shapeero wanting his own yes men in there. He also dumped Hale who I believe is still fairly highly regarded.
With Gibbons gone, they are much easier moves to make.