Lizard said:So, how many successes do you need to break a succubus' charm? How many failures until the king tells you to get lost and orders his guards to attack you?
THAT'S the kind of mechanical detail needed to make the system work -- and that's what the OP views as an anathema (and the MM doesn't seem to think of as necessary).
Rubbish. I just think it's part of adventure design, not monster design, and is likely covered in the DMG, not the MM.
Consider a possible seduction ability that's written out in the MM:
Seduce Mortal: Daily. Cha vs. Will; if this is successful the seduced mortal will follow one suggestion of the succubus per day; if the Succubus successfully uses this power on the same mortal seven days in a row, further successes are automatic and the mortal will follow any suggestion of the Succubus automatically. This may be broken by the Break Seduction ritual.
Now, how much of that is actually useful in the adventure? Only the very last sentence! And then you have additional problems if it falls into the hands of the adventurers (I polymorph into a succubus and take all her powers!) All the actual usage of the power is off-screen. If you actually use the power against a PC (and properly) then what you get is a way of turning a PC into an NPC which is NOT FUN to the extreme.
As it stands, the succubus does have abilities it can use against the heroes (and in a non-campaign-destructive fashion), and the plot-abilties are left up to the DM. The one thing that is left out is "how do you break the succubus's hold on the king?" and that is part and parcel of adventure design. Standard D&D players will be very happy with "Kill the succubus", but for the DM who wants a more epic plot (and the designers at Paizo are happy to oblige) then you can have the find-the-artifact gambit.
If it does boil down to a non-magic issue and it's just the succubus's skill use, and you "just" have to persuade the king that he's been misled, then we've been explicitly told that such interaction is handled in the DMG... and the Succubus does actually have a skill rating. Of course, the default succubus isn't brilliant at it, but she does have all the Charisma skills at their default level.