At the end of the day, it's not for me to make the determination of what is needed or not in a committee's mandate. What I will point to again, though, is the discussion in Procedure and Practice regarding the particular role of public servants. Political staffers have a different role than the one of ministers.
The general advice given to committees is to seek the information they need, but treat all witnesses with courtesy and ensure that no unnecessary harm is caused to any individual or any public policy consideration.