That’s a fun hypothesis, but is there actually data supporting (1) that “a vast majority” of westerners misperceive country size in this way, and (2) that specifically such a perception causes them to consider foreigners to be unimportant?
Although implicit bias exists, studies show its impact on the real world is much smaller than commonly believed.
And now I would like to see some data, peer reviewed study, or similarly supported source for this statement.
Because I don't see many people claiming that greenland or antarctica are super important powerhouses in the world.
I'm not sure there could even exist a particularly satisfying source for this. One of the issues with "soft" sciences is that it can be quite tricky to measure any effects, much less design a viable study that demonstrates causation.
I suppose a social scientist (i.e., not me) could support this claim using ideas from psychology or finding related studies. But I doubt anything will ever be particularly convincing unless we lived in a universe where people told the objective truth and a mandatory survey was asked with the explicit question, "Have the distortions induced by map projections influenced your beliefs regarding people in other countries?"