Yeah, there is sort of a narrow road between "follow all these rules to the letter" and "give us something we've never seen before". Objectively, my novel is very much a generic rehash. It just happens that I've been writing urban fantasy since the 1980s (mostly for my own amusement, a couple of things done for presents) as I love the genre, but now what used to come off as fresh and original is just the norm for the genre, alas. I'm still writing what I love, though. In the case of genre, I'm aware the odds are tilting slightly more against me given my subject matter.
The next thing I have in mind to write (aside from this stupid fanfic idea that won't go away) is more original and has fascinated me since the beginnings of the concept occurred to me a few months ago. To stay on topic, it's a genre-buster so the optimal length will be hard to determine, but the question of length doesn't come up for me until the first draft is done. So I'll write the thing, see how long it is, check out the market at the time, and adjust accordingly.