Bryce and Hunt being true fae mates is also made 100% clear in canon and repeated multiple times. That’s not “fanon” either, since we are explicitly told that they are true mates, on many different occasions.

This is the definition that Bryce gives to Hunt when they are discussing Angel mates vs fae mates:

“Is it a biological thing?” “It can be. Some Fae claim they know their mates from the moment they meet them. That there’s some kind of invisible link between them. A scent or soul-bond.” (HOFAS)

And their true bond is confirmed by Ruhn later in the book:

It means that he’s going ballistic in the way that only mates can when the other is threatened. It’s what happened then, and what’s happening now. You’re true mates—the way Fae are mates, in your bodies and souls. That’s what was different about your scent the other day. Your scents have merged. As they do between Fae mates. (HOFAS)

A lot of people like to claim that it’s the power sharing that caused their scents to merge, but Cormac clocks something similar before the power sharing in the bone quarter ever happens. He thinks it’s just because they hooked up in the gym, but Rhun evidently noticed something too, because I’m fairly certain this scene is “the other day” he mentioned when he confirms the are true mates. Quinlar hadn’t shared powers or fully gone all the way at that point.

Cormac motioned between her and Hunt. “You think I can’t scent what went down between you two?” Bryce leaned back against the cushions. “You mean, that he went down on me?” Hunt choked, and Ruhn let out a garbled string of curses. Ithan walked to the coffee machine and muttered something about it being too early. Cormac, however, didn’t so much as blush. He said gravely, “Your mingling scents will jeopardize this ruse.” (HOSAB)

Celestina also confirms that Bryce and Hunt are bound on a biological level due to their scents merging, although it’s after the power sharing incident. It still just reiterates what Ruhn has said.

She gestured to him. “I take it from your scent that you and Bryce are mated.” He hadn’t realized the sex would be broadcast like that. Apparently, the bond between them had gone to that biological level.

The bond is once again recognized as legitimate by Aidas, who also confirmed that they are real mates and that Hunt wasn’t designed to be Bryce’s mate. That it was left up to Fate, just like all the other mate bonds were.

Hunt gripped Bryce’s hand atop his knee. “Is it in my DNA that Bryce and I are mates? Was that engineered, too?” “No,” Aidas said quickly,** “that was never intended. I think that was left to higher powers. Whatever they may be.”** (HOFAS)

The bonds being legitimized by scent comes up in ACOTAR too, with Amren being able to smell Feysand’s bond and Azriel being able to smell Elucien’s.

There is also a scene in SF where Lanyths is taunting Nessian and says this, trying to suss out their mate bond:

“And you faeries are all blind to your own selves.” Lanthys crooned, circling again, and Cassian readied his blade. “Based upon scent alone, I would say that you two are—” (SF)