It is not in fact easier to write badfic, or even spoof-fic, than it is to try to produce something good. It is easier to write short excerpts of almost anything. No doubt if I tried to sustain badfic over a thousand words that would present its own challenges. Fantasy!Bunter is at least proving not too grim so far. Mind you, he still has most of his clothes on.
I have not been managing to write the Wimsey/Potterverse crossover, but I have at least been thinking about it and it is developing reasonably well. I now have the “they meet at a party” scene so beloved of Potterfic (not least me. The percentage of my Potterfic involving parties is embarrassingly high), and a bit of jokey RPF has turned into plot. It is always pleasing when a random idea becomes thematic. I still need to work on the purpose of the Corsican bandits, though.