I thought I’d add my experience with the Files app. I’m using a Gen 6 Lightning iPad, the Lightning SD card reader and the Files app. I’ve used iOS 13 and 14.
I travel 4 to 6 months each year. Probably take 20,000 images per year of which the vast majority go from sd card to iPad using the Files app. More specifically, using Files, I copy images from the card directly into the Adobe CC folder. I do not use Lightroom for this.
In my 10's of 1,000's of images, over 100's of discreet transfers, using the Files app, on old and obsolete hardware, with iOS 13 and 14 I’ve never seen a corrupt raw or jpeg file.
I haven’t read the entire thread but I sure don’t have any issues with the Files app.