I think the key idea Testing misses is that everyone else knows that some edit ideas have pros and cons, it’s just that they’ve independently made the judgement that the pros outweigh the cons for the specific purpose of their fanedit.
Like Leia’s lightsaber being purple in Ascendant: yes, it does make it less similar to Anakin’s saber and thus perhaps slightly less Skywalker-y if you’re really clutching at straws, but it also a) is a nice tribute to Carrie Fisher, b) better distinguishes the two lightsabers on Exegol so they’re easier to keep track of, c) breaks up the sea of blue on Exegol, d) makes Leia’s saber distinct from Anakin’s in the same way Luke’s green saber is, etc. I wouldn’t use that change for my own fanedit because I generally prefer to stick with canon saber colours, but there are many compelling arguments for it, and having one possible downside doesn’t instantly negate all of those.
At the end of the day, fanedits are alternate versions of the movie. We’re not sat here planning the new Official Special Editions to forever replace the originals. It doesn’t really matter if someone wants to make a change that you personally think ruins the movie because you don’t have to watch their fanedit. This is all doubly true for ideas like the one Nerevar is floating, where the whole point is that it’s a big change to the movie and the fun is in discussing how it would work and what the ramifications would be - it’s not being proposed as a definite total net improvement that must be implemented. It’s more of a “What if?”.
It’s also extremely condescending to act like any one person’s ideas about the films are the only correct ones. Star Wars has always been somewhat open to interpretation and means lots of different things to different people. This is true of all film (and art in general). It’s not even uncommon for art to resonate with people for reasons entirely unintended by the creators: Data in Star Trek has been seen as a relatable character for autistic people even though he was never written that way deliberately; and similarly Dax’s struggles as a character who used to be in a man’s body but is now in a woman’s body is something trans people relate to, even though that wasn’t necessarily on the writers’ minds in the late 90s. There’s no right answer, and insisting there is and that everyone else must just be stupid is just a really unfortunate lack of empathy.
Even if David Lynch sat down one day and suddenly explained at great length the reasoning behind every decision he’d ever made in his films and TV shows, people would still continue to discuss their own personal take-aways and ideas, right?