What @rob_marshall means to say is .. you can set upper level to READ only and not Hide it... Ofcourse we know that parent will have selective access enabled if children has it, but if you chose READ at the upper level you can see the aggregated data.
Your understanding is correct, I am fine to show the summaries at B. But the ask is, we dont want to show the all the list items of C(list items under B) since it will create some confusion to users. Can we show the summaries at B level by Selective access enabled , can we decouple and show the summaries? Please suggest an approach