The urge to make so-called “Fixfics” is strong among many fanfiction authors. They range from well thought-out trimming of the excesses to destroying the themes of the canon work in favor of cheap wish fulfillment. Take a guess which is more common.
That being said, I’ve both seen and hoped to write multiple fixfics. It’s tough, and depends a lot on the setting. One of the reasons why people gravitated to the Familiar of Zero setting is that it had a unique concept and strong foundation (fantasy set in a Renaissance setting, detailed enough background) and squandered it on silly antics. That was a good setting for a fixfic. There are bad ones too.
Some settings aren’t just adverse to fanfics overall, but especially to fixfics. Exactly what clicked when I was struggling to come up with a plausible fixfic of the infamous The Big One, remembered I was having similar struggles with the equally infamous Gate anime, and saw how oddly similar the settings were for a technothrilller with only one awkward supernatural element and a fantasy.
Both are horrifically nationalist works. Both go a step farther than the common patriotic thriller and work extra-hard to keep their nations from facing the slightest actual threat. And, most crucially, both have horrible worldbuilding that’s either uninspired, in the service of said “prevent conflict ASAP”, or both.
This makes fixfics tough. An author has to change a lot to make it more plausible/interesting, but that begs the question of why they wouldn’t just go the full length and write an original story unencumbered by all the baggage the existing setting has?