Oh, gosh. I don't really have different fandoms, but this:

I've realized that almost exclusively my preference tends to line up with the more morally ambiguous/evil of the pairing being the one fucking the good one.

resonated for me, ahahaha. No surprise I agree with you on this important matter. I wonder though if it would transfer to other fandoms? Answer: probably. When I've read Johnlock, I like a toppy!Sherlock, although as usual, it's not the specific act so much as the dynamic. The act itself is not to be sniffed at, though, haha.