I don't think that anyone argues that it doesn't the value of an ad impression is directly tied to the purchasing power of the audience it's presented to.
That said this is "somewhat" mitigated with local ad partners.
People from Indonesia will receive ads that are provided by local ad partners and while their spot will still be considerably cheaper this is regional pricing rather than pure valuation.
A US user is just as worthless for an Indonesian advertiser as an Indonesian user is to a US advertiser.
Companies have regional pricing to deliver products to markets that cannot afford it movies and games cost considerably less in China, Russia, South America etc. than in N. America or Europe, ads are no exception.
Also whats up with Indonesia? they have a GDP 4 times that of say Ireland, the individual income is still quite low but as far as Indonesia as a country goes they probably have bigger purchasing power than many European nations.
Also it really depends on what you advertise because in many places you can't disregard income inequality if you are talking about countries with ~300M> people they might have more "rich" people than many other smaller European nation so while the average purchasing power within a country isn't that impressive it's actual purchasing power might be quite considerable.
One thing that I've at least noticed on the few ads i did managed to receive while being in China, HK, India and the Philippines is that instead of ads for Spotify, GoPro, or Clash of Clans I've received ads for luxury watches and high end cars more likely than not because due to the income inequality in said countries if you are accessing content from a high end device you aren't just middle class you are very wealthy as many of those countries don't really have a traditional middle class (China has one now and it's one of the biggest consumer of luxury goods in the world).
The Ad market is complicated, I wouldn't just go around sticking prices to users from different countries because it's much harder to estimate that, logic that works in western developed nations quite often fails everywhere else.