So? The whole point of a battle is to not get injured and defeat your opponent. Knowing that Hidan can fodderize him with a single scratch doesn't change the fact that Asuma was too weak to prevent Hidan from tagging him, and all his effective moves are close range. So there's no getting out of this one.
Asuma has 2 medium ranged jutsu that can do nothing to Hidan. Hidan already canonically tanked Ash Burning, and I don't recall the other one you speak of, but I'm pretty sure it's nothing spectacular.
Asuma is not agile enough to prevent getting tagged. But with full knowledge that's not it, even if he gets tagged, he knows that he must not let Hidan gets the ritual.
Hidan can't kill Asuma without the ritual IMO since he lacks the feats. So with full knowledge it's:
Asuma still can't prevent getting tagged -> Hidan gets blood -> Asuma tries to prevent the ritual
To kill Hidan, Asuma knows he must get close to him since med range jutsus would get tanked, so losing blood is unavoidable. But is it the end of the battle? That's what's being argued. The ritual must be performed yet.
-Asuma can use burning ash to blind Hidan instead of burning him
-Just checked the manga and the one i tought it was asuma's wind jutsu it was ten ten with the sage's weapon