Is footage recorded through external recorder really better?
Unless the DSLR/Mirrorless camera you are using outputs 10-bit 4:2:2, using an external recorder to up-convert the footage to ProRes HQ will not result in a better image quality than what the camera is able to produce/output.

If anything it will allow you to edit and re-compress the footage multiple times without losing the original quality.

Using an external recorder may result in a better picture quality compared to the internal encoding, because there is more bitrate available per frame, more robust codecs, and also being able to remove the 5, 15, or 30 minutes recording limitation the camera may have.

A bigger plus using an external recorder (or display) is the ability to nail the focus, assess proper exposure, and having multiple eyes monitoring the recording.