Dickens wasn’t a realist in the modern sense. He created his own universe and populated with more diverse types than any other writer since Shakespeare.
Is that WHY he used newspaper articles and Henry Mayhew's books ( LONDON'S UNDERWORLD and MAYHEW'S LONDON ) as basis for many characters, as well as his fictionalized own life for his novels?
You might just as well then claim that Dominick Dunne's books weren't "realistic".
What about Dickens' best friend, Wilkie Collins' works? Are you going to tell me that his characters weren't just as "diverse", if not more so?