You are arguing a bunch of hypotheticals that couldn't possibly be proven until maybe (but probably not) revealed much later in the story to argue against the current evidence that is actually present.
Everything so far points to it being a Black Blade. The examples you provide as to why it might not be a black Blade aren't convincing.
The only real example of a weapon not being what it appears to be is Who's Who's comically small dagger. It fits with him being a former secret agent that would have used trickery to one up opponents. Funny thing is, Who's Who is using it exactly as he would use a sword anyway because his
Rokushiki skill set allows him to have greater range than whatever he is physically wielding. Like
Rokushiki makes Zoro think of Kaku as a four blade swordsman because Kaku can just flat out use his limbs as blades.
Fujitora's cane was always going to obviously be a cane sword. Cane swords are famous, Fujitora has a samurai aesthetic and his entire character design is based on Shintaro Katsu's portrayal of the famous fictional blind swordsman Zatoichi. The actual subversive creative decision would have been to make Fujitora's cane
just a cane.
The Fujitora example is especially dangerous for you to use because his entire character is an homage to an actor's portrayal of a fictional swordsman.... Which is what Aramaki's character is as well. Aramaki's character not being a swordsman with a sword would again be like Fujitora's cane not being a sword. It ruins the obvious cultural homage.
Cracker's "fake" swords are functionally just swords. Swords not made out of metal, sure but they are functionally swords that are exact replicas of a metal sword anyway.
That last one with Cracker really kills the entire thought process because there can just functionally be non-metal swords that act exactly like swords. Pump enough
haki into it and it is a
Black Blade.
All your other arguments are "what if" arguments against "what is" arguments.
What if?: "What if it's made out of wood? What if Greenbull is mocking samurai? What if Greenbull just has a fake one cause he is insecure?"
What is?: "Greenbull is carrying a sword, a blade if you will. It is black in colour in all drawn media, a black blade if you will. Chances are, it is probably a
Black Blade."
You are literally just inventing stuff with the "what if?" arguments.
Hey, what if Greenbull's sword was actually made of the bones of his dead former Cipher Pol agent girlfriend who died while she had her
Rokushiki activated thus giving her bones the properties of steel thus allowing her bones to be melted down and reforged into a blade for Aramaki to smite his enemies with? What a what if, huh?
See, I can pull fanfiction out of my arse too. Now try arguing against Aramaki's thematically unique girlfriend metal bone sword.
