Most countries are in full control of their own monetary policies and financial systems.
I don't know that they are. I think governments are quite constrained in what they can do. We live in a global economy, every nation is tethered to every other nation, there are no isolated economies. The world is dominated by multinational companies. The financial crisis of 2008 had an effect on every economy because they are all linked. If the US crashes, Europe doesn't escape unscathed, neither des China, Russia, Japan, and so on.
So bitcoin is global and borderless just as multinationals are global and borderless. The difference with crypto is that its decentralised. You don't have a few multi-billionaires deciding to skim off huge profits and let the rest of the world burn. Like it or not - and some people won't - bitcoin is a brake on the selfishness and rampant avarice of modern capitalism.