It is not unique to this case that how we divide and understand langauges is tied up with politics of nationalism. Have been since the start of modern nationalism. What we call "Italian" could be called "Florentine", it wasn't spoken in all of "Italy" until it became a political project to make it so...

And...

> Until about 1800, Standard German was almost entirely a written language. People in Northern Germany who spoke mainly Low Saxon languages very different from Standard German then learned it more or less as a foreign language. However, later the Northern pronunciation (of Standard German) was considered standard[4][5] and spread southward; in some regions (such as around Hanover), the local dialect has completely died out with the exception of small communities of Low German speakers.

> It is thus the spread of Standard German as a language taught at school that defines the German Sprachraum, which was thus a political decision rather than a direct consequence of dialect geography. That allowed areas with dialects with very little mutual comprehensibility to participate in the same cultural sphere. Currently, local dialects are used mainly in informal situations or at home and also in dialect literature, but more recently, a resurgence of German dialects has appeared in mass media

https://en.wikipedia.org/wiki/Standard_German

"Because it's basically a dialect OF English."

I'd suggest not, it is a peer / sibling of Modern English, and descended in parallel. Northumbrian Old English eventually became Scots, due to the 'English of the Lothians' using it (and eventually 'Inglis').

Go read some older Scots from around 1600, you'll probably have a harder time of it than the same age English because they were and are distinct. Modern media, a lack of formalised spelling, and simple economics post union has probably been the major factor in its slow decline towards death.

So Scots (in its various dialects) and Geordie/Mackem/Northumbrian are I'd suggest dialects of the same language, not being English. Speakers code switch between them.

You've also missed out the other language, which was spoken in the 'Old North' and the Kingdom of Strathclyde - i.e. the Brythonic speakers.

Making hard and fast statements about a topic even lifelong experts don't feel comfortable making a conclusion about is unwise.

There is no meaningful line between a language and a dialect, and it mostly comes down to politics.