The President of the PRC is not a dictator, but the first among near-equals of an oligarchy, a ruling council called the Standing Committee.
The only real answers here would be Putin, Trump or Merkel.
Trudeau is not influential enough, and neither is Macron at this point.
Xi has consolidated power to a degree not seen since Deng if not Mao. If your characterization was ever true it certainly is not now. China has been quick to fill the leadership gap left by Trump with regards to sustainable development and the one belt one road initiative. Forbes clearly enjoys a little sensationalism so imagine the top 20 will look like this:
1. Xi Jinping
2. Angela Merkel
3. Vladimir Putin
4. Donald Trump
5. Emmanuel Macron
6. Narendra Modi
7. Pope Francis
8. Shinzo Abe
9. Bill Gates
10. Janet Yellen
11. Justin Trudeau
12. Jeff Bezos
13. King Salman bin Abdulaziz
14. Mario Draghi
15. Larry Page
16. Jean-Claude Junker
17. Mark Zuckerberg
18. Theresa May
19. Jamie Dimon
20. Jack Ma