Of course there are original ideas. "C is not an original idea, because it's just mixing A and B..." ok so there are only two possbilities:
1. Someone else did mixing A and B before. Okay then we can recursively find the first person who mixed A and B.
2. No one else did mixing A and B before. The "Mixing A and B" is a new idea.
For some incomprehensible reasons, people seem to accept "mixing A and B is not a new idea because A and B already exist." Like... why? Since the four basic nucleobase existed, there haven't been any new DNA creatures?
The real reason that it feels like there isn't new idea is simple: the "mixing" process happens gradually. Even if you come up with a really good "X + Z" idea, people (read: market) might not accept it because what they're familiar with is "X + Y".
So you put a bit of Z to make "X + 0.9Y + 0.1Z", and another person who is as smart as you makes "X + 0.8Y + 0.2Z"... then when "X + Z" is officially a thing, people outside think you smart-ass guys were all just copying & pasting each other.