Don't show grouped field data in the regular list.
If you're grouping by a field (for example project name on the work items page) the project name is shown in the group area and can be sorted there. Remove this field from the grid since it's already shown.
Will have to check and see if the pivot column can be removed from view. We use a 3rd party component that, while very flexible, may not support this.
In the meantime, a possible workaround is to move the pivot column to the right-most column in the view, thus, it’s no longer taking up visible space. Not sure if that’s helpful or not.