As someone who worked on Terrys show from 1973 to 2006. Here is what really happens.
Until his untimely death a few years ago, It was Paul Walters (TWs producer) who selected the music for the show. Paul (A pretty damn fine guitarist in his own right C/W stylee) had to go by the strictures of daytime playlists. but occasionally he would sneak one in under the Radar. Eva Cassidy is the obvious famous artist here). Terry would have never have heard of Eva without Paul. But having said that, his playing her records certainly contributed to her (postumous) fame.

Paul and I would have long conversations about music of all types during the show, and he was always enquiring about my work.
So it was Mr Walters who guided Terrys opinions. Terrys job was to make it sound like they were his idea!

And yes, It was me who played Jour D'Ete on the show, just before I retired.

As for other Folk Friendly DJs. The already mentioned Stuart Maconie (who was slightly stunned when I played Candee-i-o once, him being a huge Nic Jones fan!
Mark Radcliffe, Johnnie Walker, Bob Harris, Aled Jones (Yes Really!) Simon Mayo. Jeremy Vine.

Have had conversations about music with all of them over the years.
The problem is that their musical tastes are strangled by the dreaded playlist.

Peel was the obvious maverick, with Kershaw a close second. Then there is Late Junction...Mike Harding for entry level stuff. (You're hardly likely to follow the Chris Evans show with Sam Larner are you?!)

So, to end. It's not that bad at the Beeb. It's just that daytime presenters are forced to stick to the guidelines. Hope that clarifys the situation.

Ralph