The bold part is irrelevant.
The whole point is that artists on those labels were mainstream successes.
And afterward, artist from everywhere else knew the South was here to stay.
How is it irrelevant? They were only hot because of the label. They weren't mainstays.
Neither CMR and No Limit signaled The South was here to stay. They weren't even here to stay. You could make a solid argument for CMR, but everybody knows Wayne/Drake/Nicki CMR isn't the same as Hot Boys/Big Tymers CMR.