I see what you’re saying, but:
This narrative is older than what you’re talking about, because it depends on when people argue when hip-hop “died”.
Way before the Snap/Ringtone era, people using this narrative were talmbat Bass and bootyshake music being bad for the game because a few records would blow up every now and then. Cuts like “My Baby Daddy”, “Raise The Roof”, “Back Dat Azz Up”, “Who Dat” & “Whistle While You Twurk”, et al. The narrative was:
“Look, all of that music got its place - but it’s not supposed to be as successful as it is because it ain’t Real Hip-Hop”...like Hip-Hop wasn’t invented at and for parties.
And the other side of the coin is that a lot of rappers of The South had lyrics but they didn’t get their proper due simply because they were Southern. I will admit I am biased - I don’t think T.I., Ross, and Jeezy are that great as rappers. It baffles me that they get more props than Eightball & MJG, UGK, Mystikal, Tela, Thrill Da Playa, and some others. IMO, I think that is people overcompensating for the South rap they didn’t listen to back in the day.
When would you say it took hold? I know there was a heavy anti-south bias in the 90s but I don't remember actually hearing "the South killed hip hop" argument until the mid-to-late 00s. But that's me, as someone who lived up and down the West Coast with brief stops in the South and on the East Coast. We moved around a lot in the 90s and I wasn't really on the internet like that until '99, so I found my perception of the 90s decade differs from others depending on where they were at.
When I mention Wayne, Luda, TI, Ross and Jeezy, those are the dudes from the South who were popping when I first remember hearing the South killed it narrative. Whereas UGK, 8Ball & MJG, I was checking for both heavily from Riding Dirty to the Bad Boy album Ball & G did but their time had kinda passed by then. I remember No Limit and Cash Money getting shytted on heavily by the "purists" but NY was still firmly on top at that point