If I could have only one bike, it would be my gravel bike. it's OK on the road, Good on 95% of the gravel I come across, and 'so-so' on many MTB trails. When I travel, I bring my gravel bike for these reasons. But at home, I also have a road & MTB, so I choose the right tool for the job. I've ridden an IMBA Epic MTB trail once with my gravel bike - once. I'd file that under 'never again'.
For repurposing, I did covert my gravel bike to a bikepacking rig; so I suppose that counts.