They should be because that's the primary thing a mentor should be. Knowledge is absolutely useless if a mentor isn't helpful.
I've been mentoring Sprouts for many years. Dungeons are rarely an issue. How do I read the mini map? How do I open the big map? Where are all the city aetherites? How do I know which of my gear is the best? How do I glamour? How do I dye? Can you take me on your mount? How do I drop flags? How do I unmount from a two-seater? What's a Chocobo porter? How do I unlock Chocobos porter routes? What are the differences between the quest colors? Why are the blue ones important? How do I unlock PotD? When do I get my Chocobo? How do I get my Chocobo to fight for me? How do I change the Chocobo colors? Where do I get dances? What's the Goldsaucer? How do I do Gates? How do I get a race Chocobo? What's fashion report? How can I buy a house? How do I make Gil to buy a house? What's the difference between Free Company and Grand Company? Where is the FC chest? How do I rank GC? Which crafter should I start with? Why should I become a crafter? What are leves? What are beast tribes? What do I get for doing beast tribes?
These are all questions I've explained to Sprouts several times. Literally none of that requires me to know anything about dungeon mechanics.
I've been playing this game for 8 years without taking any breaks. I've done most of the things that can be done at least once and know about the things I have chosen not to do. I don't do savage or dungeons unless I have to or I want a certain reward. In 8 years I have run less than 1000 dungeons or raids. There are plenty of things to do in this game besides only "dungeons and savage." I'm a housing decorator and I'm into glams other than following the story or getting into lore from side content. I know a lot about the game and believe that I've been a good mentor.
There are plenty of people who would be excellent mentors who don't run dungeons and no, they are not in the very niche group that does only savage content. The game has a huge RP community. There are housing enthusiasts and many glam enthusiasts. There are bards and dance groups. There are lots of screenshot artists. There are people who spend all their time at the Gold Saucer. There are lore fanatics who do every content just for the lore, as well as completionists. There are marketboard economists and now we even have island sanctuary experts (which is basically a stock market game). And of course there are people who are just interested in the story. All of these people can be great mentors without running dungeons every day.