>>3946>Do you think that would make this story better, or worse?
As to this I can't really say. It goes back to what I said earlier in >>3897
about subjective and objective definitions of artistic value. If you look at the first image of Derpy, it's objectively well drawn. However, some fans might find things in this image to object to. Some might not like the idea of sexualizing poners. Some might call attention to the fact that her eyes aren't crossed and it's wrong for the character. Some people might not like the quasi-photorealistic style and think that the MLP characters should always be rendered in the Flash style of the show. These would be subjective criticisms of the work, based on personal taste and opinion. However, the objective quality of the artist's skill can't really be called into question even by people who don't like it; whoever drew this knew what he was doing.
If I were trying to teach you how to draw, and your art resembled the CWC drawing in pic 3, I would be trying to teach you how to technically draw well and would be focusing on things like horse anatomy, proportions, scene composition, lighting, etc; what you ultimately chose to draw once you learned how would be up to you. Once you reach a skill level in any creative discipline where no one can shit on your work for objective technical reasons, that's the point where you can afford to tell haters to fuck off if they don't like it. But you have to reach that level first. If you create something that is objectively bad and
contains elements and themes that are likely to be controversial with fans, and
you choose to take a combative tone with your critics, you're basically going to get shit on without mercy, which is what has mostly been happening in these threads so far. That's why I want to try to convince you to focus less on what specific elements you want to have in your story for now and more on how to lay it out and tell it, and how to build quality characters.
Whether or not your actual idea is "good" is subjective. When you're writing a fanfiction your primary audience will mostly consist of fans of the canon story, since people who don't like MLP probably won't read fanfiction set in that universe. The more you deviate from canon the more likely you are to get pushback from people who want to read stories that follow the spirit of the original work. However, that is not to say that writing a more transformative work that makes significant changes to the universe is necessarily bad just because some fans wouldn't enjoy it. What is far more important is that the story is well written and well told. An MLP story where Applejack has laser-beam eyes and Rarity is a cyborg with a thirst for human blood would be a huge departure from canon, but you could still make a fantastic story out of it if you constructed and told it well. By contrast, a huge amount of fanfiction has been written that follows the series canon perfectly and is still cringe-inducing and awful, just because the person writing it had no idea what they were doing. Even a stupid idea is salvageable in the hands of a good writer, and even a great idea can fail miserably in the hands of a bad one.
If you want my personal subjective opinion, I tend to agree with >>171363; that it doesn't make much sense to give a character powers that she wouldn't reasonably have. If you're going to have the Mane 6 plus Silver be a party of fighters, it makes technical sense to keep them all at a consistent skill level so they can all participate in battles. However, the problem you've got with these characters is that they weren't originally designed for that type of role, and figuring out fighting abilities for all of them will probably become an awkward task the more grandiose you want your battle sequences to be. For instance, Twilight is pretty easy to level up since her whole character is that she's a strong magic-user to begin with. However, the same can't really be said for Rarity, despite her also being a magic user, as she mostly uses her magic for domestic creative tasks and probably has no interest in learning high-level spells. Fluttershy would be a huge challenge, since it's completely against her nature to even fight in the first place and she really has no combat abilities to enhance, so you'd have to probably give her a weapon of some kind, which she'd look awkward trying to use. If I were writing this, I would probably drop this idea and go a different direction. However, that is not to say that you necessarily should do the same.
I would say your challenge, if you want to pursue this idea, is less a matter of figuring out what abilities to give these characters specifically, as figuring out why
they acquire the abilities you choose to give them. That's really what's going to make the difference. Like, let's say just for fun that you decide to mount a gun turret to Fluttershy's back and have Angel Bunny man it like she's a WWI fighter plane. Is it a stupid idea? Very. Funny, but extremely stupid. However, you could still potentially sell it. What you have to think about is Fluttershy's personality and character. What could happen in this world that would make her determined enough to engage in a battle on that level? It would have to be something huge, world-threatening. An evil on the level of Sauron, something awful and dark and destructive enough to make an otherwise docile, loving and gentle pony take up arms to fight for everything she holds dear. If you just say "I'm going to give Fluttershy a machine gun because it would be cool or funny" the audience probably won't buy it, unless you're writing something deliberately parodic or silly, which I don't get the impression is what you want to write.
Focus on learning characterization first; build characters who have genuine motivations to do the sorts of things you want to have them do, then you can focus on what powers you want to give them.