I think it would help to be clearer on what the point of this question is. The "best" way to "describe" western europe and north america will be the one that misses nothing about those places and risks no generalizations, inferences, or explanations.
Like, if the goal is simply to come up with a description of n. america and europe that attends to all of the particularities of those continents, then I suppose the answer is something like this: we should make a stack of every novel, every photograph, every sociological study, every census, etc., etc., etc., ever produced by those regions, and just absorb all of it. That way we won't miss any detail and we won't make any wrong judgments about those zones.
But clearly that would not do any of the analytical work that we need to get done. The problem isn't to come up with a term that is unassailable in any and all matters of detail, but to figure out what conceptual problem we are trying to address in the first place, and then to see whether it is addressable in terms of a dialectic between (say) the global north and the global south. That's the only way we can come up with a helpful terminological distinction.
I think (though I'm not certain) the problem you're trying to get at is something like this. We know that North America and Western Europe stand at the center of a global process, of which colonization and modernization are discrete yet inseparable moments. They stand at the center because they are the perpetrators and beneficiaries of colonization.
But the "strange" thing is that although these zones used resources stolen from other zones in order to become wealthy and industrialized, the people who live in europe and north america do not uniformly benefit from that theft. Another problem: at the same time, colonized and formerly colonized nations are not uniformly underdeveloped. There are pockets of vast wealth, industrialization, etc., to be seen in many other countries.
This doesn't mean we have to throw out the opposition between the two (which would only make it harder to understand what is going on). It means we need a way to talk about it that takes into account the multiple contradictions implied by colonization and capitalist development.