Dances With Wolves is one of the few films in which a voiceover actually works for me.
I think that has a lot to do with the fact that he was voicing the words that he was writing in his journal and that the journal itself was significant to some of the events in the film.
Not that any of this is relevant to the movies actually in this HOF.

I can definitely see how thinking out loud what is written makes for a better narrative when you're not a fan of characters narrating. It definitely makes for a valid exception.
For myself, with Costner, (being late to the party) I've always enjoyed him in a larger number of films as well as his directing. Dances With Wolves being the very top of his game for both. His mixture of epic storytelling and delving into the characters' personas has always been a pleasure for me.
With Narratives, I've pretty much enjoyed them since childhood. Not sure if it was the cartoons where characters talked to the audience or the serial style oldies like Flash Gordon and the like along with shows like Batman where the Announcer teased us about "how will our hero get out of THIS one?" or even Shakespeare where the Narrator and Soliloquies were commonplace.
No idea, but I've even come to enjoy the mocking narrations like in Kiss Kiss Bang Bang.
times it can become a bit of a trope, but, like @
ahwell stated,(as in anything) when done right. . . I quite very much enjoy them.
Which is an amusing irony since there is not narrating in an HoF I'm hosting, as Miss Vicky pointed out. lol