No matter how good your fanfic is, it will never be a replacement for the original.
No matter how good a fanfic with Ash having a Nidoran instead be, it’ll never take the place of the original, even if hypothetically it could be better.
I’ve been guilty of this with reading FIM fanfics and only watching of FIM said to myself, “Gee why couldn’t Faust have made characters this good?” Without even knowing what FIM was about or that she made the universe those fanfics were in in the first place.
As someone who wants to write my own alternate version of FIM, I want to make sure I dont have the nerve to suggest the other FIM is outdated.
Even if the author writes badly I think its important to awknowledge your story is a derivative.
And at the same time, a fanfic might not please everyone. Some might prefer a ship. Or someone not to die. But in the end its not your fanfic. Its theres.
You can write fanfic of that fanfic if you prefer but dont think your it will replace the original.