The character is so thin, her motivations and inner-life so poorly sketched, that the internet created a whole insane conspiracy theory to make her interesting. The last week was filled with rumors that the Waif would end up being a Tyler Durden-style figment of Arya's imagination. It's fan theorizing at its dumbest: an attempt to patch up lackluster writing by inventing an elaborate twist that will never happen. Rather than admit the show's creators might have made a mistake, we wrap ourselves in theories to bolster their infallibility.
It's hard to blame anyone. In the end, the Braavos arc felt like three episodes stretched across two seasons, basically stalling Arya's inevitable -- and highly anticipated -- revenge tale so that the rest of the characters could position themselves. There was no saving the Waif, who kept the wheels spinning by repeatedly berating our hero. In a show filled with hateable people, the Waif is probably too boring to be the worst Game of Thrones character ever. Even when it comes to being the worst, she is not the best.