all sort of combine into a Schrodinger's pairing with Bruce in some sort of gen-limbo.

This sentence just made me so happy ;o)

admiring a friend or relative is different than admiring a(n ex)mortal enemy

That's really interesting. Although, I think that depends on the reader as well, because I do think some people have a stronger tendency to ship enemies or people who have animosity than others. Most of my ships tend to be those in which the characters feel and instant connection and are drawn to each other, and then as they try to work through a relationship something comes up between them. Obviously, Harry/Draco is an exception (although I don't think Angel/Spike is necessarily an exception. I think one reason I like it so much is how Angelus and William were totally into each other and then fought. But my major BtVS pairing is always Buffy/Angel, which is obviously no exception to my stated preference).

I'm also inclined to think canon relationships are gen

I sort of think so too. I mean, no one's going around saying Pure and Simple Truth should be het, even though Ron/Hermione exists and actually plays a rather large part in the story.

I think A Fine Spur is less gen than the others just because the Natasha relationship is the only one

Welllll...Bruce's relationship with Steve is the only relationship in The Hollow Men. There are some other characters, but Bruce is fairly arm's-lengthy with them.

Bruce is more restrained with Tony or Steve

I do mean to write him that way, so I definitely figured Bruce/Natasha would come across more strongly than the other two.

Thanks so much for your thoughts!