So So Def alone...
Usher TLC Da Brat Xscape Jagged Edge Kriss across and Jermaine Dupri himself all made waves to push Atlanta to the forefront as one of the truly major cities for 90’s black music, it was So So Def and LaFace who Outkast Goodie Mob and Usher TLC we’re signed to who did this, in many ways the two were linked to each other to the point you could be ignorant to think someone like Usher was actually signed to So So Def.
OutKast in the 90’s was just a single group, JD already had Kriss Kross come through and smash the buildings before OutKast had a hit, by the time OutKast blew proper he was still making waves with Usher, Jagged Edge and even Lil Bow Wow.
I guess if we’re solely talking rap we can make arguments but even then ATL only took the rap scene in the last 15 years with the likes of Gucci Jeezy Lil Jon and co, OutKast in many ways were outliers.
Usher and TLC were not So So Def artists. Jagged Edge wasn't really a big deal in the 90's. They didn't take off until the '00's.
Your timeline is off because Kast two platinum albums by the time Jagged Edge dropped their debut in the 90's.
Outkast was just one act, but you want to talk about movements, let's talk:
1) OutKast went platinum, which opened doors for Dungeon Family as a whole, which included Goodie Mob and Organized Noize
2) Organized Noize, after producing Kast's first album, went on to do "Waterfalls" for TLC, which is possibly their biggest song. This was the biggest single off their best selling album which greatly helped catapult them to one of the biggest female groups in music ever.
3) Goodie Mob came out in 1995 and went gold
4) Kast dropped their sophomore in 1996, which quickly went platinum scoring them more gold singles and a #1 rap single. The same year, Organized Noize produced a #1 single for En Vogue, which was one of their biggest singles. Organized Noize is also brought in that same year to produce what would be Curtis Mayfield's last album.
5) Kast and Goodie both drop albums in 1998. Goodie goes gold again and
Aquemini is Kast's biggest album both commercially and critically in the 90's. It went 2X platinum despite none of the singles being bigger than the singles from their previous albums.
6) Goodie Mob drops another gold album in 1999. Cee Lo Green appears on Carlos Santanna's album from that same year for which he receives a Grammy. Big Boi appears on albums from Slick Rick, Missy Elliott, and Young Bloodz. Kast produces and appears on songs for Tash, Mystikal, and Eightball & MJG.
By the time Jagged Edge and Bow Wow really blew, Kast was easily bigger than both.
Kast in the 90's were bigger than anyone signed to So So Def. Organized Noize in the 90's were rivaling JD as producers.