He does not ever actually alter any particular universe in the sense of erasing a given outcome, but rather moves himself to a universe where a given outcome never came to pass.
Right, this is what I meant by a POV timeline.
There was a...I'm going to call it a Wizard of Oz fan novel (I am unsure of the author and how "canon" it is) where the main character--I'm going to call her Alice--is given the power to go back in time, but she can only alter a single past event. She inadvertently prevents the king of Oz from doing something stupid (drinking from a fountain--I forget the exact details as to why this is important), and as a result the Emerald City is instead the Obsidian City (complete with black glasses instead of green*). So she goes back in time again to stop herself from stopping him and can't find the fountain. Goes back in time again and again, looking all over the forest for the fountain, cloning herself hundreds of times (cue image of a dozen Alices all running around and bumping into each other).
Eventually Alice figures out hint that the "power" of "only alter a single event" is actually a curse that
actively prevents her from making more changes, and gets the hint that there's more than one way to view time. So she travels back in time along her
own personal timeline rather than the objective real-timeline and is able to not-alter the past (by choosing differently).
So that's what I meant by a single non-branching timeline: Marty's personal timeline. But as far as I know, there's no single entity in the Zelda universe that can experience all the outcomes of the Zelda branching timeline.
*That's a thing that wasn't shown in the movie: when you entered the city you had to put on special green-tinted glasses. Very obvious to the reader that that's how everything in the city has the shade of emerald.