Thanks @kerley I was playing devil’s advocate of course, but you are right, it’s not so much a question of the bike as whether I enjoy riding back roads and simple tracks enough to make it worth buying a bike for the purpose.
I’ve tried those rides on both my MTB and road bike now and neither work. The MTB is too slow on road to be enjoyable for more than a short while and I have to nurse the road bike too much on the tracks to avoid destroying tyres and wheels, so that’s not much fun either once the novelty wears off.
I have found some lovely little sections of track, through woods, by streams etc. But without the technical challenge would they get boring too after a while? I suspect not. I enjoy exploring more than tech these days and a gravel/adventure bike does look like a good option for that.