World’s busiest air routes, 2017.
1. Jeju to Seoul
2. Melbourne to Sydney
3. Mumbai to Delhi
4. Fukuoka to Tokyo
5. Rio de Janeiro to Sao Paulo
6. Sapporo to Tokyo
7. LA to San Francisco
8. Brisbane to Sydney
9. Cape Town to Johannesburg
10. Beijing to Shanghai
Here is the source. Via Henry Farrell. It is striking how poorly America and of course Europe fare on this list.