Allow me to compare this situation to mystery stories, anon. The concept of mysteries fits perfectly with the Masked Royal's identity
Edgar Allan Poe's "The Murders in the Rue Morgue" is one of Poe's best works. In my opinion, it is only rivaled by "The Tell-Tale Heart" for my favorite Poe work. In "The Murders in the Rue Morgue", the killer is much implied to be one of the many suspects in the story. The curveball comes in when the killer turns out to be a stray orangutan that broke out of the zoo.
This is a perfect ending to the story, as it is unexpected. Similarly, if the Masked Royal isn't Kukui, then it would have a similar effect, being a well deserved surprise and a good ending.
"Death is a Lonely Business" by Ray Bradbury, on the other hand, is a shitty novel. In the novel, A. L. Shrank is a short, nihilistic librarian who smells bad, hates everyone, has a short temper, looks like the aforementioned Poe, and has had many failed businesses. It comes as no surprise when he turns out to be the killer.
This is the worst possible ending to the novel, as it makes it all a monotonous and boring race to the end of the novel. There is no sense of suspense. Similarly, Kukui being the Masked Royal has the same effect. It's boring and too expected.