I don’t know what your second example is referring to.

Quotes from Chairman Mao, the very apotheosis of a victor writing history.

Seriously, how is that an example of history being written by the victors?

HP is a fantastic glamorization of elementary students growing up during the domestic fascist turn in the wake of WW2. It isn't simply a story about wizard kids, but an allegory describing liberals coming of age during the 60s and 70s. The heroes and villains and side-characters are all fictional re-imaginings of period figures. Had the English come out on the wrong side of the World Wars, you'd likely be reading a similar set of books translated off the German, telling a similar coming-of-age story about growing up in post-war globally dominant Germany as a young wizard coming of age with evil (((monsters))) hiding in the school basement that only a clever and talented Draco Malfoy could grow up to defeat.

History is not written by the victors. It is written by those who are most able to write history.

The folks most able to write history are the ones in the position to conduct research, formulate a narrative, and distribute it most aggressively. Those people are inevitably working on behalf of the most wealthy and influential business and political interests in the region. Aka "the victors".