The countries in power didn't change much in size, but the countries they controlled did. I stand by my point, if this was the other way around and a useful projections shrank everything near the poles (and Africa looked much bigger on the map than it already is), those people would likely dislike that projection. They would ask themselves why it was so skewed, while now it was no issue. It is a coincidence that Mercator works that way, but it is no coincidence they liked this one so much.

Saying it was just handy is downplaying the strong sides of other projections. Take a look at maps from that period and see how many inaccuracies there are, because they had no satalite to check how right they were. Navigators weren't stupid and they would easily understand how to navigate another projection if Mercator was disregarded for some reason.

Take a look at historic uniforms, the amount of jewelry etc; people have been vain since the beginning of time and have always cared about the looks of it. I honestly can't imagine they would have been fine with a map were they seemed smaller than they actually were, i can easily imagine they would be glad to use a map that showed them bigger then they are.