Johnson's closest comparison is probably Arnold Schwarzenegger. Both entered the acting world after achieving success in completely unrelated fields, both rely on presence and charisma to carry their roles, and both have become the most bankable actor of their generation. They are very similar in many ways, but there are some key differences:
Comedy is a key skill for a charismatic actor. Both Arnie and Johnson thrive in the "action comedy" genre, but Johnson has much better natural comedic timing. On screen, he's often funnier than the professional comedians he shares a movie with.
Johnson has also drastically improved as an actor throughout his career, while Arnie has never been able to better his early roles. If you watch Johnson's early films, like The Scorpion King or Doom, you can really see how much he worked and perfected his on-screen character. He has also taken on more directly dramatic roles in projects such as Pain and Gain and Ballers. Is he the best dramatic actor in the world? No. But he is certainly believable and no worse than many other actors.
Furthermore, Johnson is also a successful producer, having produced several films and television shows. Her experience and his knowledge in the world of entertainment have allowed him to develop successful projects and manage them effectively.