Lighter,
I'm sure most of what you say is correct and your comment about fudging describes well the impetus behind numerous PhDs. I was just stirring the possum about the (apparent) requirement for there to be written literature before a language could be recognised as separate; it put all the oral-only ("prehistoric" according to some definitions) languages out of consideration as languages.

In Australia we have had a long tradition of white fellas (mostly from Europe, including the British Isles. but also from North America) arriving here and telling us 'what's what'. Until relatively recently, all Australian and PNG languages were thought of as just dialects; in uninformed 'popular' discussion they are still dismissed as such by many.

But I don't wish to divert an interesting discussion.

Cheers, Rowan