Six onion-roof towers supporting heavens

[bi3mw]

Why on earth would we expect consistent scales? 

Yes, it is hardly possible to expect proportionality and correct scales. The decisive criterion for the representation of image elements was often simply their importance. In the Catalan world atlas, for example, the flags are more important than the buildings themselves. The oversized depiction of the ruler (Mansa Musa in your image excerpt) also makes sense in this context.