The idea of a consolidated imperial core is in itself flawed and the idea itself is not applicable to all situations. Though definitely a useful point of view sometimes, using it unconditionally will only deny nuance and differences between core countries, which is not always helpful.
EDIT: Guessing this will probably get downvoted and/or ignored, but if anyone is actually willing to provide or cite some justification/explanation of the map in question, that would be great. Linking the Wikipedia article, whose map differs and has the reasoning of core countries as
They are usually recognized as wealthy states with a wide variety of resources and are in a favorable location compared to other states.
containing several points, which in total are inconsistent by leading to a false dichotomy, is not what I ask and not what I think a map of imperial core states should use for classification.
My reasoning for calling a consolidated core flawed is among other things because it is not taking into consideration the historic development and relationships between core states. Some classify, for example, Scotland as a semi-core due to these reasons.