Agreed.
With mods in Darktide, you can do little beyond gaining hidden information, changing some minor things like visuals and weapon sights or adding a flashlight to your gun, and (apparently, although I haven’t seen evidence of this) shoot a gun like some kind of robot in a way that a simple macro can’t.
If it were possible for a modder to come into my game, throwing infinite grenades and blowing everything up or shooting forever with infinite ammo or just deleting every enemy or teleporting me under the map like I’m in a damn GTA lobby, I’d be inclined to agree that there’d be a clear, objective line in the sand…because those mods would “directly affect unmodded players’ experience of the game and/or is used to grief other players”.