What I get from your opening post is not that “bronies have bad taste in Fimfictions” but “bronies don’t like the things I do”.
Rightly or wrongly, “dark” (or, more disparagingly, grimdark) as a genre has certain negative connotations associated with it, viz-à-viz quality and I would say those connotations are more rightly deserved when it comes to fanfiction.
Cupcakes is an extreme example but it perfectly highlights the problem - the drama is completely overblown to the point where it’s more amusing for how poorly it’s handled. And all too often it’s easy to fall into that trap of trying to darken the tone of a story but instead of making the drama realistic or in some way relatable, it’s obvious that the author just doesn’t grasp how to do it.
I’m hesitant to say this because of how insulting it is but, again, there is an assumption out there that violence (at least the overwrought and needlessly explicit kind in Cupcakes) is the purview of adolescents taking their first steps in fanfiction.
Is it right that people make such presumptions? Well yes and no. Time is the most valuable commodity and in trying to get a reader to read your work, you’re basically having to sell it to them in exchange for their time. Glossing over a poorly made, grimdark image might earn a roll of the eyes but only because artwork is immediate. Reading a story takes time and effort in concentration and the emotional payout can take a while. Because of that, having wasted so much time on a poorly written fic is naturally going to stir up a stronger response.
So of course people are going to be wary after being stung on poorly written dark fics. And because it’s so easy to get wrong, there’s proportionally going to be more of them (IMO).
In that way, I agree to an extent with Scygnus but obviously not for the same reasons. It is easier to read something short (and comedic or sexually explicit, etc.) but that is, again, because you simply cannot ignore that the time invested versus possible time wasted isn’t quite as much an issue as it is with something longer.
The absolute worst thing you, as a writer, can do (and I’m speaking from experience here) is make your reader come away from your story feeling like they’ve wasted their time.
As others have said, however, you also cannot discount how much of a departure it is from the tone of the show itself. I’d prefer not to speculate on how many enjoy it for its light-hearted tone but for the purposes of this discussion, I would say it’s quite a sizeable number.
My favourite fanfic is Twilight Sky Over Canterlot. I read it when it first came out and have loved it since. I’m going to spoiler the next few paragraphs for anyone interested in reading it who hasn’t yet. || It is, for all intents and purposes, just Twilight taking a trip back to Canterlot and reconnecting with ponies she’s met and known, as well as her home. But it’s more than that. It’s a glimpse into how we can touch those around us so deeply and profoundly, without even realising it or knowing just how much our little actions mean. It’s suffused in the kind of nostalgia that’s whipped up upon revisiting one’s old home and haunts; about realising that that nostalgia doesn’t have to overtake us.||
It’s been easily over a year since I’ve read it so many of the smaller details elude me right now but I must stress that for its richness and depth, the structure is incredibly simple. Yet it has been used to great effect.
Ultimately, what it comes down to (as the above is an example of) is being able to handle your chosen subject. Sometimes, yes, it is the idiot public not appreciating your magnum opus but sometimes, too, it is because you only see your baby.
