First time I see Germany classified as “a corner of England”, lol.
(To be fair, before the current crop, the English aristocracy spoke mainly French, and I guess France could be classed as “a corner of England” by people still a bit hung-up on the loss of Brittany...)
RP English is heavily influenced by French and Germanic tones. Local dialects are very different. I still find it hard to compare British languages with what developed in North America, where the influence of non-English-speakers was clearly massive. Isn’t it more interesting to look at Australia and South Africa, where direct links with English natives are way more recent, and still the language departed markedly...?