Believe me, this doesn't happen all the time. Most fandoms fall into the balanced category. That's not surprising, since the coming of the Internet has spawned a huge number of fics out there. Yet the ratio could apply to the days of zines-only. Why does one fandom attract good writers while others do not? A question that comes back to chemistry. Why do some pairings appeal to people while others do not? Sometimes you can reason it out, but many times it's like love: no one really knows why.
So I find myself enjoying an amazing number of well-written fics. And the variety of them is delightful. I'm enjoying my favorite pairings, Clark/Bruce and Bruce/Dick, and also I've found Clark/Dick and other pairings not written quite so often. I'm enjoying comedy, drama, angst, darkfics, deathfics, adventure, PWPs, AUs, and so many wonderful genres. I like to sample all that I can, rarely refusing to read a fic due to theme. Some people avoid dark or deathfics. I feel there is a place for them, and the well-written ones are joys to read. The Batfamily seems to have more than its share of darkfics, which I suppose is its nature, but there are happier moments, too. And the light of Superman? Darkness can dwell there, but no matter what an author chooses to write, the crafting of the fic in this fandom is so well-done. Have I found fics that could use improvement? Sure, that could be any fic, but what impresses me is the low level of mistakes or a theme clumsily handled. Consider ourselves lucky, my friends, as I've seen good fandoms saddled with low-quality fiction. Praise to the DC fanfic writers! :)