My wife’s father is British, born in Rhodesia - his father was born in Leicester, and registered his birth as British. Her oldest brother was registered as British at birth in South Africa, so has citizenship and a passport. Her birth, for some unknown reason, wasn’t registered as British, or they did it too late - regardless, she’s a naturalised South African, and all she was entitled to was an ancestry visa because of her British grandfather. I came over as her dependant, and after 5 years on the ancestry visa and then holding ILR for a year, we’ll soon be applying for citizenship.
Not sure if Breytenbach’s argument has any legs, and you may eventually only be entitled to an ancestry visa via your grandmother (if she was born in the UK).
This is my route right now, it's so expensive (NHS x4)