I agree with your general point, but I'll quibble with your example: Maturin and Aubrey love women and do not share a home, or even a cabin on voyages. Sure, you could write fanfic in which they sneak off for some quality time, but you'd have to be a mighty fine writer to make that fit with what O'Brien gave us.

Slash with Holmes and Watson is easier; all you have to do is assume Watson is bi or more closeted.