I made a video comparing the sound of a song with the default Camera app VS Open Camera (with different audio input settings):
Default audio is good when simply talking to the phone, but absolutly not when singing or playing music. But, as @corvuscorax pointed, “unprocessed” audio usually needs to amplify the gain to get a decent/normal audio level (I found that you can do it easily in Audiofix, but it would be really nice if you can choose the entry level or a kind of auto input level).
Maybe the good thing of the low audio signal in unprocessed is that maybe if you record live music events with this configuration, audio will be good and not distort (“clip”) the signal 