The Threat Roll resolves the consequences of the threat, not the Scoundrel's own effect. The Scoundrel has whatever effect that's been established, regardless of the Threat Roll outcome (unless you include the threat of failure).
So, On a 6, you avoid the threat. That means it has no effect on you.
On a 4/5, the consequence is reduced. So in your example, level 4 Harm would be reduced to level 3.
Ok. So if the threat is that “the billhooks are Unreasonable (narrative T4) in their demands - not only is it an absurd quantity of coin but more” and the player faces that with say Sway they’ve talked their way around it on a 6. So if you wanted to structure a more demanding challenge to something like the players wanting the Billhooks to run interference for a smuggling operation or something; you might go “ok, with your going in position they won’t back your play - at best they’ll just let you way as you move through their territory (effect) and they’ll be Unreasonable about the bribe they require for even that (threat).”
