A and C - good point but whilst instructors are hopefully great on the flying skills often they are not as familiar with the idiosyncrasies of the groups' type - obviously it does depend what it is and how complex it is.
I think it is important to remember that a group check out is not a GFT, but it is about exploring the flight envelope of the type I would have thought.
Having said that hopefully the group check pilots will have done their C of E's or IMC / IR renewals on type. If they have they well have picked up some good points from their FI.