Editing a video's exif in Apple Photos makes it impossible to export it to desktop/Finder in full quality

This all started when I was using Photos on my iPad to manage all my photos and videos. I've noticed that moving the videos (from my Lumix camera) from Photos to Files app reduces their quality (about 1/4 of original size, with visible compression artifacts). I didn't find a solution to that problem, but I thought that maybe macOS will do better in this regard.

Now, on my Mac I think I've finally found what's causing that - it's editing the exif data of my videos (it's necessary, since they always appear 1 or 2 hours too late. Even worse if they're imported from a different program).

Example: I have a 99.7MB 4k clip imported to Photos from Lightroom. It has a wrong time on it - LR export time, not the actual time I took the video.

a) without changing anything, I drag this video from Photos to my desktop. The video keeps the same 99.7MB size

b) I correct the exif data inside the Photos app. If I drag it to my desktop now, it ends up being compressed to 59.7MB (although it's still 99.7MB in Photos)

Is this how it's supposed to behave?