It’s just that links in different places have different dune formations (due to geology and climate) and different vegetation. And since the historic term links was first used in GB&I, it could be argued to refer to its type of land.
I just want to have terms that make sense. I agree with you that they are completely arbitrary, but they can be arbitrary and useful, or arbitrary and confusing. Where we draw arbitrary boundaries around the term we affect that usefulness.
I will fully concede that if we start with the linksland of the Scottish lowlands and work outward, we will see slowly changing features as we move farther away. Some localized changes, however are dramatic, as the massive dunes of a Royal County Down will be non-trivially different from sand bar, like Portmarnock, which are just 56 miles apart.
If we then want to put an arbitrary line between say Rye and Wimereux, just 38 miles across the channel from each other, that's all well and good, but that line doesn't represent a substantial change in climate, flora, or fauna. I will concede that we have a Ship of Theseus problem here. If we want to make the definition essentialist or arbitrarily geofenced, contending with that is arbitrary. However, if we base the term around the collection of features themselves, what I've been arguing for this whole time, then we may have some quirks here and there, but we have a consistent and useful term.
I can let this go, I feel like I've already push this past the limit of even my patience. In the end, I'm a descriptivist, and the vast majority of people are already using the terms the way I think they ought to be used, so it's effectively moot anyway. I just think it might be helpful for the golf community to come up with useful terms to guide people to understand what they are getting when they play a links, links-style, links-like, or just linksy course.
Not all dunes are formed by this process. Inland sand dunes, even non-river mouth dunes found along the ocean, such as the
Namib Desert (seen
here), are formed by completely different processes.