Having a loud personality and a toned down personality is not the same think as not having a personality at all. A lot of these underground rappers lack personality, while rappers like Kendrick Lamar and J. Cole has toned down personalities, more like "real people". While other like Gucci Mane, Rick Ross or Busta Rhymes have very loud personalities you'd get laughed at if you had that type of personality without being a super star.
Any rapper with success has a personality, some a bit more humble, gentle others a lot more "look at me", "the world evolves around me" type of personality others just a funny personality, swagged out, overly corny etc.