I think this is the correct analysis - the focus should be to provide vaccines to the rest of the worlds nations that have not yet gotten widespread access to vaccines. This is likely to cause the greatest benefit in the form of fewer global deaths, and reduced global spread of the disease.
There is no evidence that we have to choose between boosters or sending vaccines to other countries.
This is the same flawed logic that officials made when they spread doubt about the effectiveness of masks early in the pandemic, hoping to “conserve” masks for healthcare workers.
The assumption of vaccine scarcity is actually a hidden assumption made outside the expertise of those who aren’t deeply knowledgeable about vaccine supply chains.