Hi!
I agree in the sense that the relevant element is not the case, but the quality of the person who gives the case! This is far far more important than the case as such. There are loads of people out there who get very damaging feedback from non- or ill-informed case partners, and this is how many damaging habits and practices become a "common feature" of whole generations of applicants.
In my view it is important that a candidate gets proper guidance/coaching from a competent person (consultant who does interviews/ ex consultant who was trained on interviewing / coach from preplounge) very early on in the process, as this will then make subsequent peer practice sessions much more helpful (where the candidate then already has some perspective and is aware of how cautious he needs to be with peer feedback).
Cheers, Sidi