Wealth is a relative measure, not an absolute one.
"That's like saying that the last person (blah)"
No, because relative to other people, they have more stuff. The proportion they have of the group's net worth is significant greater than almost all other members, who have generally have five or more orders of magnitude less wealth (0.0000005% and less).
The reason why you're having trouble converting from countries to individuals is because there's currently only 200 countries, but 7 billion individuals. That's why the individual's percentage looks lower.
Also, your comparison makes absolutely no allowance for inflation. GDP rises for everyone over time simply due to inflation. Your shekel could purchase more in the time of Herod than it could in the time of Netanyahu. Zimbabwe's GDP went through the roof in recent years in their own dollars; but it didn't as a comparison to the rest of the world's output.