With Avantgard, it is clear that supers exist in other nations on Earth. The events creating super-powers are NOT limited to just the USA.
But, since we aren't reading about super-incidents in China (which houses roughly a third of the Earth's population), the indication is that most "super potentials" go through their lives without exhibiting any manner of super-powers whatsoever.
If I'm understanding the fluff correctly:
1) Not every human being has the potential to be super. In fact, fewer than one in a thousand have this potential.
2) Not every potential encounters a "stress event" that activates their powers. The majority of potential supers live normal lives.
3) Not every potential survives the stress event, and a significant portion suffer physical or psychological damage from the process.
4) Most superheroes are not "weaponizable", either due to lack of power level or powers unsuitable for combat.
Some manner of resident trauma (psychic residue energy) seems to be created with every super origin. This energy seems to encourage/generate/be generated by violent crime. So either superheroes and supervillains rise because of the breakdown of society, or at a certain level of chaos there are more "stress events" that generate heroes. The issue gets thornier if the USE of super-powers generates this dissonant energy.