I've happily done 100km of gravel on my '89 Fisher and would choose that for anything gravel/ light single track that could be done on a gravel bike.
But having tried a modern bike on modern trails... I have to admit things have moved on. I got my first mountain bike at 8 in 91, rode and raced through the 90s, was riding a full sus by the end of it. Then didn't really ride mountainbikes (other than occasionally my Dad's 2003 Rockhopper). Was put right off suspension for a long time.
I've reluctantly decided a modern mountainbike, but in steel, wouldn't be the worse thing to have to ride modern trails and in all honesty if I was riding a long mountainbike route.
It's fun to ride the Fisher, it performs better than any bike I owned in the 90s, clearly having been somewhat ahead of it's time. I can still rip trails on it, but it's not as comfortable. Still gives me satisfaction to overtake someone on a full sus on a downhill though!