There seem to be 2 types of camera apps for the iPhone: those aimed at adding filters and post-processing; and those removing all processing & automatic controls that the stock camera app wants to add (by default the iPhone software will want to apply lots of corrections, "improvements" and change settings on the fly that can make a video or photo look terrible).

This is the latter, handing back control of the camera settings to the user, which is what you want for consistency of the look of a video whilst subjects move, the camera pans, etc...

In that case, you don’t understand it. This isn’t preprocessing software.

It’s mostly aimed at getting the right shot in the first place, and giving skilled users enough control to make better shots.

So that’s why it’s called camera.

Because it is not postprocessing software, it's a camera app

Also seems to allow setting manual settings during filming. Not sure if that is possible in the native camera app on iPhone.

No, it's a full on camera app.