Yes, I know -- the question stands: why would you have both of these concurrently in the same system? Either you want a KDF, or you don't want a KDF -- pick one

Yes, I know -- the question stands: why would you have both of these concurrently in the same system? Either you want a KDF, or you don't want a KDF -- pick one, and don't start reinventing your own (potentially poorly), please :-(