Tim Hardin may have been more self-consciously contemporary and less tied to older traditions than most other singer-songwriter soloists of his era.

At the time, in the US at least, he was still classified and pretty universally accepted as part of the "folk music" scene ~ certainly moreso than Bobby Darin (who straddled many different genres), and also moreso than someone like Paul Simon (who came along a little later).

I believe the fact that Hardin generally played solo, relying only on his own acoustic guitar for accompiment, was enough at the time to make him be seen and accepted as a "folk" artist. That, along with his very personal vocal style, which was decidedly "folky" in contrast to the Vegas-lounge-act approach that was still fairly mainstream at the time (and which was really Bobby Darin's first love).

I was glad to see someone mention Fred Neil, a similar artist from the same time and place and another personal favorite of mine. Both of these guys were phenomenal singers, possessed not only of great "pipes" but also the ability to convey deep emotional expression in their singing. Both could probably have been quite successful interpreting/covering traditional songs and/or songs composed by others, but both were also excellent songwriters, prolific enough to allow each one to perform original material almost exclusively.

Both died too young, too.

"There is thread on mudcat at the moment - what is being sung in folk clubs. If you believed that lot, you'd think every bloody folk club in England was an annexe of Cecil Sharp House."

I think that the content of thread is a kind of self-fulfilling prophecy. Steadfast traditionalists would seem to be more likely to submit their set lists to it than others. I briefly considered posting a response of my own, but didn't do it because I'm not in the UK and my repertoire is so different from what the OP was looking for as to be irrelevant to that discussion.

What I play could best be described as 1960's American folk-scene nostalgia, including traditional country blues (mostly John Hurt), some Dylan songs and other similar "contemporary folk" from 30-40 years ago (including a few Tim Hardin songs, of course), and a lot of borderline pop/folk, country/folk, and folk/rock, etc. If I like a song well enough to learn it, and assuming that I can find a way to present it with my acoustic guitar and my solo voice, I'll give it a go.

I have no prejudice against newer material, but I'm a slower learner than I used to be, and I have an existing 60s-70s "frozen in time" repertoire because I was an active full-time performer back then, before taking a few decades off to slave away at a day job and raise a family...