I imagine this is obvious to anyone who's reads Malus' past comments on duels, but it isn't going to happen. Not in a million years. People have very personal opinions about duels, but it's a feature of the game that I feel has been twisted by weird, anachronistic notions of romanticized nobility, like Aaron Burr dueling Alexander Hamilton or something.
"You shall retract your slander!" 'I refuse!' "Sabers at dawn, sir!"
No thanks. I created the idea of blood debts exactly because it seemed stupid for a duke/ruler/priest to go dueling knights, lords, and lower nobles. A man or woman of power doesn't, IMHO, whip out a sword and demand satisfaction. They leverage their resources to suffocate, kill, or drive off their enemies. Ain't that right, Brom/Ramiel/Norrel/Arundel/Finsternis? I think Malus even made that comment to Brom, when he came knocking for a duel.
"Pick up your sword!"
'But I have a thousand. I have an army.'
It is stupid for a person in power to duel when they can just leverage their resources instead.
Malus's comment, although not worded that way exactly, as Brom's request wasn't, but in general the concept is correct. However, Brom was essentially in a desperation swing. He didn't expect Malus to accept, but was hoping that he would be stupid and allow Brom to save face and essentially be restored back to power in Luria. In the meantime, he used the distraction of dueling and accusations to prepare his leave from Luria.
Same way he used the impending assault on the city of Giask to prepare his leave from Luria the first time.
What else would you expect from a Machiavellan pragmatist?