Economic leverage leads to other type of leverage, geopolitical and potentially even military. China needs a lot of commodities (food, feedstock, grain, meat, metals) etc. that they can import from SA, while simultaneously exporting cheap electronics, EV's, solar panels, and everything in between to SA. The military port was just an example, the real threat would be if all of this trade was going to be settled in Yuan rather than dollar. If that happens, that would be a gargantuan blow to the dollar, i don't think people understand that. It would also mean that those countries will start to 'listen' to those that have this leverage, possibly at detriment of our national interests. The point with China, is they can push us out because countries like Brasil find they are a better economic partner vs the US, god forbid same happens with Mexico. They don't even need to pick up arms or start wars, they can just offer better trade deals than we can, that's why i don't even know how we counter that.
But reality is, eastern Europe is not of critical importance to us. It was 50 years ago when the big bad beast was the USSR, not today. Pumping the Philippines or some other SE/East ally with defenses is way more critical than eastern Europe, like it's not even in the same ball park close. Yet here we are today the MSM screeching that we can't 'appease' dictators and we absolutely have to keep fighting in Ukraine. The longer this goes on the better for China, because it redirects valuable limited resources from where they need to go to basically waste, as if Russia is more than a regional power at this point in history.
My point is that it's not possible for China to gain that sort of leverage over Canada or Mexico. They're both well within the gravity well of the US economy. The US economy next door is too large a market for it not to be the dominant influence, except in a world where the China has won the GDP so decisively as to make the entire question moot. In any case, you'd see the United States "assert its interests" with Mexico well before it ever got to that point.
The US dollar has a pretty deep moat. For all of its problems as a reserve currency, there's no faith in any of the alternatives. You're either at the mercy of the Chinese government or the EU regulatory state. Neither has a great track record at growing / protecting individual wealth.
I agree that the EU is no longer strategically essential. At the end of WWII it represented the only other major base of industrial production in the world. Now there are many, and the EU regulatory state has created a lot of daylight between the European and American economies.