Nah, you're right. I rescind my objection.
Also to
Buttons12345 suggestion I have to say that countries giving up land voluntarily is something that I always missed. NL giving up Luxembourg for whatever reasons, preferebly gaining something else, but intimidation works as well, would be really cool. You should also be able to bribe countries or threaten them into giving up land but still giving them money so it looks a bit more like a deal and less like a robbery or something similar to that. Might fit into this hybrid of gunboat diplomacy and economics that the 19th century is famous for
I think gunboat diplomacy (or more generally aggressive diplomacy) is a mechanic that Victoria 3 really needs. Yes forcing minor nations into unequal trade agreements, sphering, or turning them into satellites, but even civilized countries. Perhaps have diplomatic intimidation options that increase threat and potentially (Germany won't be intimidated by Denmark) improve deal improvement threshold. I think the best way would be to have some sort of intimidation option to any diplomatic offer, and if you have nearby military units it will increase acceptance threshold based on the size of the force and the disparity and national power. If Germany stations 120,000 soldiers on the Dutch border and surrounds the Netherlands with its navy before sending its offer the Netherlands are much more likely to accept.
I would also be interested in seeing actual ultimatums that don't force war. Using the above example, putting all those forces around the Netherlands might add +80 to the request to surrender Luxemburg, however if Germany/NGF makes it an ultimatum it is more like +160 but if the offer is refused and Germany doesn't declare war in a set period of time (casus belli could just be "ultimatum") than they take a big prestige penalty and piss off nationalistic pops for backing down.
All of these however should massively raise threat when used on major European countries, and raise threat (albeit a lot less) when used on outside nations. If NGF mobilizes its army, surrounds the Netherlands, and gives them an ultimatum to hand over Luxemburg France should be so threatened they might immediately declare war regardless of the outcome of the German demands, while even Russia, Austria, Denmark, Belgium, and Switzerland are deeply concerned.