I really don't think it matters who's saying it if knuckles is physically present and looks willing to do it. Of course if I'm a noble at a court ball surrounded by royal guards, that threat is going to be significantly less worrisome - again, regardless of whom it's coming from.
Compare with "I think you want to do me a favor, otherwise that shipment of rare wines you just had come into the docks might have some... in transit breakages in about 5 minutes". Or "Otherwise your daughter might be involved in a nasty riding incident". Or "your wife's childbirth might be... messy".
And all of those are far too blunt to be delivered in polite company... which is why it might help to have some decent mental stats.
All of that said: while I think that SOME comparison with physical combat is perhaps appropriate, that's more for the goals and outcomes of said combat and how they contrast with most social schemes.
1. Physical combat is resolved as multiple rounds of actions by all participants.
2. Typically doing nothing is the worst thing you can do: there are exceptions where you might deliberately take a consequence to improve your position, and misjudge (ie accepting an opportunity attack to improve your position, hitting friendlies with an area effect so you can hit more enemies), but you're best off doing something and not simply saying "My character doesn't fight much, I just go skulk in the corner and let the combat guys do this".
3. While the best fights might have an end result where a single roll becomes crucial, typically more than 10 actions and their assorted rolls would have lead up to that, and it would be hard to say in the wind up which roll by whom would be the crucial one.
4. Unless the competition is horrendously one-sided, there are consequences for the victor as well as the vanquished.
5. Multiple traits matter, so different characters and monsters will have a different approach.
6. Teamwork is more effective than being a lone wolf.
7. Player decisions matter.
8. You can usually bring it back from the brink of defeat.
I think that if you want to come up with any kind of a social combat system, those are the positive aspects of the combat system you want it to bring across. 4e's skill challenges failed at 1, 2, 3, 4, 6, 7 and 8, and in my view was an awful exercise in pointless rolling as a result. Most skill resolution systems fail in the same way: the best thing for an unskilled character to do is to recuse themselves, and a very limited number of pre-determined rolls dictate success or failure.
This is exactly so. The idea is to turn *some* set piece social encounters into the equivalent of combats, where every PC has an opportunity to contribute and engage and rather than being resolved with a couple die rolls it ebbs and flows over the course of the conflict. it isn't appropriate for all social encounters, or even most, but is intended to take the place of an equivalent combat encounter while providing the same fun.
The reason i chose the distribution of Attributes and Attack types was simply because I wanted to make a scenario in which everyone was able to contribute, not just the characters with the high charisma. Modern forms of D&D, including 5E, built their combat systems to be inclusive (hence at will cantrips for spell casters and other PC class balancing mechanisms) without necessarily making everyone the same. If only Charisma and Wisdom are important (as would be the case if you only relied on the skills as they were written) then only a few characters will be able to meaningfully contribute.
In any case, it seems a moot point. My players shot the whole idea down so I am going to dump the court scene entirely. We have a large group and prolonged RP encounters where only the "face" PC does anything are a slog.