"To parley, you have to have leverage."
For the Parley move to trigger you have to have something over the NPC or something the NPC wants. Dungeon World uses the term leverage to describe this:
"Leverage is anything that could lure the target of your parley to do something for you. Maybe it's something they want or something they don't want you to do. Like a sack of gold. Or punching them in the face."
Thus the threat of violence only establishes the ability for the parley move at all. You still need to convince the target that its in their best interests to work with you, that you won't simply kill them when you are done or that you really will pay them what you promised etc.
This already exists as an advanced move for the Fighter
Available from level 2-5 when the player levels up.
As such I would suggest leaving it where it is as a fighter advanced move, vs. having this open to other classes.