Ha! Ixtila, you thought
you wrote a novel! Be warned!
It is your second paragraph I would like to address, and please take this with the spirit of debate I intend.

First, I was not comparing Joan of Arc with Zeus. In my analogy Zeus takes the place of God, or any other divinity you like to name. In Greek myth the heroes are equivalent to the prophets and saints of Christian belief - divinely empowered (or blessed) disciples (in the broadest sense of the word) of the gods.
I agree, bad comparison. So compare Joan of Arc to Perseus instead.
Joan of Arc was an actual historical person. The historical record regarding her undisputedly reports she says she experienced miracles. Many of her followers believed she experienced miracles. To write historical fiction regarding her without addressing those miracles in some way is, in my opinion, to diminish the historical accuracy of an historical fiction novel.
The author could choose a mundane explanation for those miracles. Attribute them to psychology or her manipulation of those around her, or coincidence, instead of the divine. That would not decrease, IMO, the historical accuracy of the novel.
The author could choose to simply lay the miracles out there and let the reader decide if they are mundane or miraculous. Also a valid choice and keeps the novel in the realm of historical fiction.
The author could choose to treat them as Joan and many of her followers treated them, as miraculous interventions from God. This is
also a valid choice and does not, IMO, move the novel from historical fiction to historical fantasy.
Part of what I like about historical fiction is getting into the mindset of the historical people. If miracles were believed by them, then the author writing that miracles are believable is not taking the book into the realm of fantasy.
I’m writing from the perspective of a firm agnostic, by the way. I’ve no particular dogma in this hunt.
Now Perseus and all the other semi- or non-divine people in Greek Mythology are also myths. Writing about beheading a Gorgon, where we never had Gorgons in the historical record, would be fantasy. One is writing about a non-historical person doing non-historical things.
And then we come to Troy. The Trojan Wars actually happened. More people are realizing that oral legends can be passed down intact for generations. Schliemann discovered a site that might be Troy based on Homer. Things Homer described have turned out to be backed up in the archeological record. Helge Ingstad discovered L’anse aux Meadows by following the sailing directions in the Greenlander sagas. Descriptions of Saxon mead halls in Beowulf have turned out to be backed up in the archeological record. Etc, etc, etc. (No, I don’t think Grendel was historical!)
So some of the Odyssey and some of the Iliad may be historically accurate.
If an historical novelist does a lot of research into Troy and Greek history from that time period (pick a Trojan time period) and decides “These people believed in Gods. They believed their lives were dice on a Divine game board. I’m going to write my book with my historical characters acting and believing as closely as I can research to the actual historical people of that time, which includes a belief in Divine intervention” I cannot point to that and say “No, that’s not historical fiction, it’s fantasy, get off my shelf!”
So perhaps we should not be asking if Greek myths are like Christian miracles but rather if Greek myths are more or less historically accurate than Arthurian legend or stories of Robin Hood. Are they fantasy or history?
Arthur’s another good example. There was probably some war hero that fended off the Saxons from some part of Britain for up to generation back in the sixth century. This grain of historical truth has sprouted all sorts of mythological matter to go with it. Some of the mythological matter is easily dated to waaaay past the sixth century (Mallory, et al). That can be pruned away. But again, an author who goes back to the sixth century and researches as much as possible (not a lot, alas) and tries to get into the heads of the people back then…that’s historical fiction, even if their heads were filled with miracles.
My problem is, how much of that sort of thing can you include before it's historical fantasy, and how much can you bring in under the aegis of authenticity in the voice of your characters and the "feel" of the setting? I mean, part of the point of historical fiction (to my mind) is to bring the past to life, and help us to feel what it was really like during a particular time. If you DON'T include the things people believed they saw during your time-period, how can you really accomplish that authenticity?
I dunno, maybe it's just like the sliding-scale between speculative fiction and literary fiction. Some books are clearly one or the other, and others are in a grey area where the readers can sort of define it for themselves.
I agree it’s sliding, and there are bunches of grey areas. I think author intent is important here. If the
intent is historical accuracy then it’s more probably historical fiction. If your Egyptians, from your research, believed that sort of thing, then it’s historical to put it in your book.
If you actually have an actual God walking down the street, you may have stepped into fantasy. But even then… Is it a vision one of your characters has? Was it an historically documented vision? (Probably Historical Fiction). Or are the Gods characters in your book? (Probably Historical Fantasy)
You could write a Trojan War tale that is gritty realism (within the bounds of what we think we know about the Bronze Age). You could put in Hittites & the Tawagalas Letter, & Akkiawah, etc. The characters are people, not superheroes, Helen is a beautiful woman, Achilles a fierce warrior, they may claim descent from the gods, but they are still just people. People die of wounds or illness, just as people do. If the story mimics a realistic world, it's historical fiction, the standard type.
Or you could write on the same subject, but the gods have walk-on roles. You could still have Bronze Age "Realism", but maybe Thetis visits, Appollo's deadly arrows strike down strong warriors. Maybe a cyclops or a nymph is lurking in the wings, or maybe they take center stage. If the fantastic elements are clearly fantastic, alongside a recognizably historical setting then you've got historical fantasy.
I think whenever you talk about genre, you're talking about style, which just isn't reducible to iron-clad checklists. I don't think anyone would want it to be. Creativity is about juxtaposing dramatic elements, creating and destroying patterns. It also starts with the artist's act of will, the desire to take a particular story a particular way. Trying to fit your personal style to some external standard just seems like the kiss of death.
Yes! I agree! And your last paragraph is soooo important.
Write your story. Write it true to your writer’s heart. Worry about what genre it’s in later with your agent or editor.
I've decided to call it (mayqueen’s novel) "historical magical realism" because it isn't really fantasy. There are supernatural elements, but only in so far as the characters believe these elements to be supernatural. (I was dealing with Anglo-Saxon and Nordic beliefs about shapeshifting and the power of spoken charms to heal.) Different readers have read these elements as totally fantastical and others have read them as completely explainable to our modern "scientific" minds.
My training as a sociologist makes me lean toward really taking seriously the fact that people who lived before us believed in magic, in the supernatural, etc. Hell, we still hold these beliefs today.
If you write a novel heavily based on that, is it fantasy or not? I don't know. Maybe that's why querying it was so damn hard.
The story I’m working on uses sung galdor as magic. It’s really magic. My story is, thus, really fantasy, no matter how accurate the historical bits are. If I was working with characters singing galdor and it didn’t contradict the physics of the universe (scrying, wards and actual weather manipulation are not historical) then it could be historical fiction. After all,
they thought the galdor worked. (Well, except for the part where William lost the Battle of Hastings so all of history post 1066 is different. But
aside from that…
I had to think a little more about what Ultragotha posted. The Merovingian has a point.
That’s Merovingian
Superhero. You have to say it in a grand voice: ULTRA
GOTHA! Ta-da! I’m sure that’s historically accurate.

Someday I will find a Superman font “U” to have as my avatar.
Let's say you do a Joan of Arc story, and it's pretty much gritty realism, except she has a conversation with God and God answers. OK, compare that with a gritty, realistic Greek tale, but someone meets a satyr in the woods. What's the overall feel? What element predominates? Talks with God or satyrs may be fantastic, but if that's just one element among many, well, is it useful to call the story a fantasy?
God(s) are historically documentable

Or at least conversations and visions are. Satyrs not so much.
A far better writer, Michael Moorcock, wrote The Warhound and the World's Pain, again with a gritty, realistic setting in the Thirty Years War, mixed with meetings with Satan, deals with God, etc. I don't think he ever had a problem calling it fantasy. Gene Wolfe's brilliant Soldier in the Mist and Soldier of Arete about Latro the amnesiac , misplaced Latin mercenary tend to get pigeonholed as fantasy, yet I can't help but feel that they have something great to offer historical fiction fans.
I don’t know that gritty and realistic would be a dividing line between historical fiction and historical fantasy. Chelsea Quinn Yarboro’s St. Germaine books have a gritty realistic feel but they’re firmly fantasy. There are a lot of gritty ‘realistic’ unabashed fantasy novels out there. Dark Fantasy is quite popular.
I don't believe that Christian miracles should be ring-fenced or above criticism (note: I was christened, but would not call myself Christian.) However, you have to remember that the people of the 1st century CE really did believe things like predicting the future by inspecting the entrails of a sacrificed bull, the Greeks truly believed that there was a time when Gods walked among them, and Julius Caesar was convinced he was descendant of Hercules.
Yes.