I beg your forbearance in advance.
BC is very social, IMO, but in a way that supports their business model: you share what you buy, what you wish for, and what you follow. Their resistance is entirely predictable as they have resisted doing anything that is not consistent with their business model.
As a person responsible for managing a web-based community, I am here to say that so-called "social" product capabilities are very, very difficult to build, maintain and differentiate. While BC has a smaller portfolio of features, what they have is very smart and tightly integrated with their core value proposition.
WRT to discovering artists, I had a long conversation with a colleague about this. It turns out we are more likely to discover artists when we linger on platforms with either lots of people (e.g., Twitter, FB) or a very focused community (e.g., Lines) or when we talk to each other. We concluded that discovery is a discontinuous function from buying.
BC does not have the critical mass of people to be a uniquely good discovery platform. But they have a critical mass of features to be an excellent buying platform.
My conclusion is people are shopping on SC and buying elsewhere, but they are discovering everywhere and buying on BC. Which platform is profitable points to which business model works.
Thanks for your patience.