I personally find it difficult to compare the cameras from your videos, since the first video shows terrible lighting conditions, which would make it hard for any camcorder to deliver decent results.
But anyways, some while ago we replaced our AX33 (that we've used as entry level camcorder) with a Panasonic HC-V777. Not exactly as good, and no 4K, but we're ...
This command preserved the colorspace and also video didnt get darker after transcoding
ffmpeg -i input.mp4 -color_primaries smpte170m -color_trc smpte170m -colorspace smpte170m -r 25 -crf 18 output.mp4
more about colorspace: https://trac.ffmpeg.org/wiki/colorspace