I think you are misinformed about the level of corp tax in most poor countries. Twenty countries have corp tax less than 15%, of which about half are poor. 15 have no corporate tax and are either rich or are just unambiguous tax havens.
Average corp tax in Africa and South America is 28%, Europe and Asia are 20%.
Most of these are poorer than G7 (and especially the US who is the main beneficiary), so my statement is 100% correct. I didn't say that all poorer countries will get poorer by this specific action. There are many other actions to make everyone poorer than the US.
And less private spending and investment by these corporations and their shareholders. The optimal size of government spending, as a percentage of GDP, for economic growth, is likely well below 25%, and significantly lower than the level in every OECD country, so to the extent that this enables increases in government spending, it will likely hurt economic growth:
Average corp tax in Africa and South America is 28%, Europe and Asia are 20%.
https://taxfoundation.org/publications/corporate-tax-rates-a...