As if "A" or "C" defined a person capacity. I know some straight A's that went directly for a repetitive and boring but well paid and stable job. Other stayed in academia and turned top scientists.

Academia is a very particular dynamic very difficult to find elsewhere, and some people dig it. You can watch some people finding the same dynamic at Google for example, where they are allowed and encouraged to fiddle around and keep publishing (e.g. the Attention paper, why would Google allow such publication?). Such dynamics are explored in Terence Kealy book "The economic laws of scientific research".