I don't think it matters what people call it. If G+ works for you, who cares if people call it a ghost town? Your G+ certainly doesn't sound like one.

If we wanted to have a substantive discussion about how well G+ is doing, we'd need to know a lot of specifics about G+ (as well as define what 'well' means in this context). Can 540 million active accounts be a ghost town? Depends on what 'active' and 'ghost town' mean. If we're just going to throw around labels without definitions or data, people just end up supporting the idea that feels right in their gut.

As defined as: "has at least left a comment on YouTube". I'm not sure I'd count that as "active G+ users".