To clarify, do you just need the parents of a set of elements and display those? Am I correct to say that you were trying to display elements excluding leafs?
If so, perhaps just via Subset, with TM1DRILLDOWNMEMBER and TM1FILTERBYLEVEL might be sufficient already. Then you can just use the tm1-ui-element-list and the tm1UiTable.create() directly.
This service was originally meant for use with what tm1-ui-element-list' output.