I was using broad approximations. It is true to say that Gaelic culture dominated in what is now known as the "Highlands", wile Anglo-Brythonic culture dominated in what is not the "Lowlands". Obviously, there are exceptions- Galloway was largely Gaelic, and the East was a jumble of Angles, Gaels and Picts- but for the sake of those not familiar with the geography of Scotland, the distinction is sufficient.
Well, like I said, the Highlands is a cultural construct not invented until later. In 1000 it is not a "jumble of Angles, Gaels and Picts" ... the Kingdom of Scotland in 1000, stretching from the Oykel to the Forth, was entirely Gaelic speaking as far as we know.
As a related point, while we prefer to call them Gaels, and to exaggerate their affinity to Ireland, they called themselves Albanach in their own language and Scoti in Latin. Before 1300, the demographic centre of Gaelic Scotland lay in the coastal regions between Fife and Ross (the kingdom's heartland was the Tay valley) ... Scotland's culture in that era was neither English Lowland nor Hibernicised Hebridean.
"Angles" ... by which you mean English ... lived in the Lothian and Borders region (about 5 % of the modern territory of Scotland) and were not part of Scotland as it was then.
Argyll and Inverness aren't very fair examples- both are on the borders of the Highlands, and so have tended to absorb neighbouring dialects, in this case Glaswegian and Doric, respectively. If you talk to someone from the West Highlands or Isles, they have a noticeably distinct, Gaelicised accent. Granted, such things are being increasingly normalised these days, but I am acquainted with a couple of twenty year old Lewisers who still sound quite different, with the result that non-Scots have occasionally mistaken them for Irish.
Basically, you are doing what many Scots with some knowledge of Scottish history do ... take Scotland as it was in the mid-18th century and eternalise it.
Gaelic is only spoken properly in the Outer Hebrides today, and that's been the case for the best part of a century. No accent in Scotland is "Gaelicised" except theirs ... otherwise accents are regional. People in Highland Perthshire have roughly the same accents as people in "Lowland" Perthshire.
I didn't say that it did. I said that the Britons of Strathclyde were of a related language and ethnicity to the Britons of Wales, and would be considered, by most of their contemporaries, to be approximately the same people, much as the the Gaels of Scotland and Ireland were considered to be much the same.
That is true. My point of contention is that this does not make this small region exception ... nor Welsh as we would think of it (but BRITISH!). All of the British Isles were or had been Celtic-speaking in the 1st millennium AD. Strathclyde didn't really last much longer than most other areas.
Gaelic and Welsh btw are similar, and were more similar in this period, kinda similar to Scots and English .... but more like Old English and Old Norse. It's important to understand that differences between Britons and Scots, as they are differentiated in the sources, may be more literary than linguistic.
