Joji Yanami is a veteran of DB voice acting. Not only does he play Dr. Brief, the King, Dr. Frappe, and Babidi, but he’s most famous for portraying Kaio-sama and the Narrator, both of which he plays in his own natural speaking voice (though with some slight inflections, depending on the situation).
My theory is this: the entire story of DB/Z/GT is being told, in retrospect, by Kaio-sama, which is why he is the narrator. Even when he refers to “Kaio-sama” in the third person, it’s a completely in-character thing for Kaio to do.
For the last several years, whenever I watch DB, I can’t remove Joji’s narrations from his Kaio-sama. And I wouldn’t want to! My theory makes it more fun! Like Kaio is telling the legend of Goku to a future student!
(Possibly a student which asked, “How did you die?”)