Well, I have never read it. Yes "C'est qui qui" is familiar. Let's say it's like "Malgré que", you shouldn't say it, it's bad to say it. Everyone says it. Politicians, reporters, teachers... But It's opinion based. It's just that 99% of the world population thinking 1+1=3 doesn't make it true.

There is exceptions, as said, but this is not good french. it really sounds bad. But it is maybe opinion based. It's like "C'est qui qui a fait ça ?" Yeah everyone says it, but it's still very bad french.