One reason to believe it (or more specifically, to believe the correlation between the Romance-Germanic axis and the difficulty axis is not zero) is that easier

One reason to believe it (or more specifically, to believe the correlation between the Romance-Germanic axis and the difficulty axis is not zero) is that easier / more common vocabulary is often Germanic and harder / more literary vocabulary is often Romance, as a result of the origins of social classes and an intentional desire to use Romance words (or straight-up import Latin words) among those of higher learning / standing. That's the claim of several comments in this thread.