I can't help but feeling like if we're just going to be talking about copyright, we've jumped the shark.

It is, in a sense, not really relevant whether a judge would or would not determine that the new driver is a derivative of the Linux driver; the point is that the OpenBSD project has no particular wish to be dragged into a complicated, fuzzy, expensive legal battle over this code. And that remains a reasonable desire regardless of the actual legal status of the work.