"it's all a question of who sets the standards, though, and what the criteria of achievement are."

The standards are set by the audience, which in the folk world tends to include a high proportion of people who are singers or musicians themselves who can judge from a base of knowledge. I suspect that for most people who are not professionals, the main criteria of achievement would be recognition and acceptance by ones peers - fellow musicians.

For the professional who's trying to earn a living, the only important measure of achievement is financial. I don't believe there's anything wrong with that - recognition doesn't pay the bills.