SW was never complex. It's was very simplistic, light vs dark, good vs evil, bad guys wear black and good guys wear white.
Its has nothing to do with complexity, the balance theory itself is just a silly notion. Why even address it? Dark vs light works perfectly. Why negate that into a "balance always wins by definition" argument that leaves nothing for drama. Is the message: just wait long enough and everything will be alright?
It also defeats the purpose of a story. Because at the end of this trilogy, when the heroes win and Kylo turns to the light, it simply means that darkness is rising in equal measure somewhere else. Happy ending.