I agree with almost everything here, but I don't think an embargo on China would be as damaging as you think it would.
It would hurt, don't get me wrong, but China is largely in the position it is now because the developed world was looking for cheap labour and China fit the bill. There is no lack of underdeveloped nations who would gladly shift their economy if it meant they could support a fraction of the manufacturing supply that China currently commands. Africa and South America (not a single nation, I know but this is true of many African and South American nations so I'm combining for simplicity's sake) is positioned both politically and geographically, to be a sudo-China in terms of manufacturing if the wider world decides to embargo China-proper.
The US and EU pulling out of China would devastated them far more than it would affect the former. I'd like to think that the EU at least, would be willing to withstand some economic damage to aid another nation in need.
I'm sorry, but I completely disagree. I don't see any evidence for this vassal worldview (apart from extreme cases like Belarus and Russia). Without that first assumption the whole premise falls apart.
Even assuming the main characters (MC) and vassals idea is true to reality, the rest of the argument is flimsy at best. Even if a MC loses a vassal through mismanagement or foreign interference, that doesn't automatically mean that the vassal has a new MC overlord. They could be in a limbo state where some of the MCs are vying for control.
As for Trump, I think it's much less of a stretch to assume that Trump loves the sound of his own voice and what better way to hear his own voice than to create sound bites, hence the 51st state nonsense. If anything Trump's actions say to me that he has NO capacity for the mental mapping required to envision this kind of complex interweaving of interests and angles that is geopolitics. I find it even less likely that this is the one he would subscribe to.