Cook the elbow macaroni in a large pot of salted boiling water until al dente. Reserve ½ cup pasta water before draining.
Heat the olive oil in a large deep skillet over medium-high heat. Add the ground beef and onion and cook until the beef develops deeply browned crumbles and the onion becomes tender. Drain excess grease if necessary.
Add the butter, garlic, 1½ teaspoons Cajun seasoning, smoked paprika, garlic powder, black pepper, salt, and tomato paste. Stir for about 1 minute until fragrant and the beef is coated in the buttery seasoning.
Reduce the heat and pour in the heavy cream and milk. Add the cream cheese and remaining Cajun seasoning. Stir gently until smooth and slightly thickened.
Remove from the heat and gradually stir in 1¼ cups cheddar, ½ cup Parmesan, and the mozzarella until melted into a thick golden-orange cheese sauce.
Fold in the elbow macaroni until the browned beef is evenly distributed and the sauce fills the curved centers of the pasta. Add a little reserved pasta water only if necessary.
Scatter the remaining cheddar and Parmesan over the hot macaroni. Cover briefly until the cheese melts across the surface, then finish with parsley.