What the experts tell you sounds great in theory. However I am not convinced. And the questions that remain unanswered may well help me decide.
It seems to me from listening first hand to tower ops at a Class D location with C above it, that while your claim they are too busy to handle the C above it is in fact not that bad at all, and in fact handling the flow from higher up makes it safer up there and at the coal face.
I have sampled this from the other side of the fence and it seems to work smooth also, both VFR and IFR.
So unless the questions of others are addressed fairly, it seems your claims from what experts tell you, while very plausable indeed, do not stack up against what I have seen first hand as an observer and participant.
You could do the same if you asked them nicely.
SQ