Apparently you don't know the history of it as well as you think then, as you can read any of the pioneers of Karate, from Funakoshi, Motobu, Mabuni, etc.. and each one somewhere will mention the definite importance of Kata to Karate training, and the fact that the kata's are built with techniques that you actually are meant to use on someone. In these guys books there are pictures of the techniques from kata being used..so i'd say it's pretty clear cut that they had a comabtive purpose, rather than just being for exercise or art.

AS far as "bunkai" itself and the idea of hidden stuff, that is a new part I think, the reason it seems hidden is that it gets practiced so divorced of context now, I imagine in the old days it was all pretty common sense what the moves 'meant'. Bunkai itself is a new term in Karate, and I think (but not sure) that it was popularized my Kenwa Mabuni.

Seriously dude, pick up a book by one of the people above, or by someone more modern regarding Karate history like Patrick McCarthy..there is no real debate about what kata's original purpose was..now, whether or not it serves that purpose for most of the people now practicing, how practical it is now,that is another question entirely. The historical part really isn't up for debate though, that has been answered fora long time.