Mike20201
Happy New Year to you too!
There are three key things to be aware of here.
One is that comparing a singular item with multiple items is not strictly incorrect. For instance, the following is logical enough.
Unlike the manager, the other employees do not have to compile daily reports.
We can tell that the manager is the only employee who has to compile daily reports. There's no ambiguity or illogic to what that sentence conveys.
That said, the second thing to be aware of here is that, in the case of this question, the point is moot, because what's really being compared in the correct version of the sentence is rates of growth.
Here's the credited version:
For the last five years the Dutch economy has grown faster than the economies of Britain, France, and Germany, and the unemployment rate has remained well below that of the other three countries.
To be honest, whether that sentence is meant to convey that the Dutch economy has grown faster than the economy of each of those countries or faster than the combination of the economies of all those countries is not clear. So, that sentence is not ideal. What would make sense is to say, "the economy of Britain, France, or Germany."
All the same, it is true that the Dutch economy could grow faster than those three economies combined. Right? The Dutch economy could grow, say 2 percent per year, while the combined economies of the other three countries could grow 1 percent per year. So, for the sake of choosing the best of the available choices, we can choose choice (E).
The third thing to be clear about here is that, in the question you linked to, the incorrect versions are not incorrect simply because a single item is compared with multiple items. The incorrect choices are incorrect because they are rather illogical in multiple ways.
For instance, the version created via the use of choice (C) conveys the nonsensical meaning that, unlike an adult, pound for pound, children breathe twice as much air. Twice as much as what? Also, multiple children breathe more air than one adult breathes? I would hope so. Furthermore, comparing multiple children "pound for pound" with one adult does not really make sense.
So, the question you referenced provides virtually no support for the idea that the GMAT would consider illogical a comparison of a single item with multiple items, because comparing a single item with multiple items is not really the issue in that question.