The way I explain them like this: Rhetoric is persuasion with logic and appeal to reason (Ob = Perception), Persuasion is persuasion with pathos and appeal to emotion (Ob = Will), and Suasion is persuasion with ethos and appeal to philosophy or religious doctrine (Ob = Will), and I think I’d say that Seduction could be treated as ‘force of personality’, up to a point.
Meanwhile, the actual Philosophy, Doctrine, Etiquette and such are ‘satellite skills’. They’re almost always related to conversations involving the former and make very good FoRKs, but can’t be used by themselves to convince someone of something.
Ugly Truth meanwhile has a bit of a reputation in my games for being overpowered because the Obs are so low compared to other social skills. I’ve limited it somewhat by saying that you ‘have to be saying something that’s definitively true, and confront the target with it if they are refusing to listen to other types of persuasion’ so you can’t just ‘make up’ truths with it as you’re suggesting. That is still the role of wises.
An example would be… You’re trying to persuade your grieving half-sister to leave the country with you and abandon her terrible abusive husband before war breaks out in France. You’ve tried to just persuade her but failed, so now you need another ‘easier’ avenue. Luckily, you’re the family bastard, and even though everyone seems to hate you, you mean well. This also means that you have Family-Secrets-Wise. So you use that to establish the fact “My half-sister’s husband is cheating on her”. If you pass the test, probably an Ob 5 or 6, then you can come back to the sister and present your argument again but this time with Ugly Truth! Because it relates to an ‘ugly truth about family’ it’s only Ob 2 to persuade her now, instead of her normal Ob 5 Will.
If you’re actually lying, then it’s either Falsehood or Extortion.
And yeah I’ve never seen a straight Will vs. Will test, except for a sorcerer’s clash of wills, or when two socially inept characters start learning how to be persuasive for the first time… at the same time.