Irrelevant.
If you are in a group or perform individually there are advantages and disadvantages to both. People like Cohen get the best of both worlds and many on the scene have done this to great advantage over the years. Martin Carthy springs to mind but there are many others. All 3 are options and you choose what works for you. I enjoy performing solo about the same amount as I enjoy being in a group. I don't think this has much bearing on the survival of folk clubs, except perhaps solo artists are cheaper for the organisers.

I would dearly love the crib-sheet merchants to learn their songs, but as they are very much in a minority I'm not going to lose any sleep over it.