Even a cursory search will find you literature from respected economists on this subject. There may be debate on how much wealth transfer or the actual impact of it, but there's wide consensus on the fact that there was. Comparing these ideas with flat-earthism is quite extremist, I'm curious if you've reached this conclusion on your own or have been led to it by some sources?

[1] https://cepr.org/voxeu/columns/economic-impact-colonialism

[2] https://economics.mit.edu/sites/default/files/publications/r...

[3] https://monthlyreview.org/articles/the-drain-of-wealth/

[4] https://wid.world/document/unequal-exchange-and-north-south-...

[5] https://ideas.repec.org/p/gnv/wpaper/unige144406.html