For musicians who self-publish with a copyleft license, they only need a fraction of their audience (those who say “Heck that’s good! In fact it’s so fricking good I’m gonna patronise them to the tune of a quid for their next work.”) to click-thru, there is no label and no sponsoring advertiser.
Because your music is unconstrained by license, web radio stations will play it knowing they don’t have to pay for it (unless they too want more of the same in order to build up their audiences). Moreover, the listeners know that they can download MP3s (or FLAC versions if they want it in high quality) without hassle and for nothing if they want a permanent record, and can give it to their friends without being locked up by the IP cops.
Unencumbered music is the future. Especially as the labels are intent on making encumbered music more expensive and more dangerous.
You’ve demonstrated that the numbers for label music simply don’t add up. Any residual viability is the inertia of tradition, and ultimately as good as pissing in your fuel tank to travel another couple of miles. Eventually it will come to a grinding halt.