In his book, A Brief History of the Samurai - A New History of the Warrior Elite, Jonathan Clements argues that, in the shadow of Occupation authority censorship of samurai narratives, ninja were more or less invented to fill the gap in popular entertainment.

With samurai still out of favour, writers and artists, particularly on the left, found a new working-class hero to lionize. Potboiler novels, comics and TV shows began to speak of a heretofore unmentioned underclass of assassins, the ninja. Considering the ubiquity of the ninja in twenty-first century popular culture, it is remarkable how fast they appear to have sprung out of nowhere in the 1950s and 1960s.

He further argues that

Any attempts to make a scholarly study of ninja lead down a series of false trails, with modern sources that end up only citing each other, and credulous populist works that claim any reference in an old account to shinobi (stealth, spies, assassins) was in fact a reference to one of several secret ninja societies that stayed in the shadows.

Is there a general consensus about the "realness" of the ninja among scholars of Japanese history?

(Clements also provides a longer argument criticizing other sources of ninja history in the notes and references of the book, which I can transcribe if needed.)