I am new to Affinity (purchased both Photo and Designer for hobby work). Previously I used mainly open-source software (digikam is my collection manager and the tool I mostly use for pictures, then gimp for editing with masks and layers and inkscape for vector work, occasionally also krita and darktable but more out of curiosity). I don't have any experience with Adobe products (too expensive for a hobbyist).
That being said, one of the first things I noticed is the extremely large file size of the .afphoto format. I concur to the comment above, and as an engineer working in SW development I can't see any justification for such a waste of space. Adding a rectangle to "frame" a 7 MB JPEG picture results in a >70MB file size! For advanced retouching of some pictures it could be acceptable, but not for large collections.
I found a few comments on the file size already in the forums, but I haven't seen any developer feedback. Is this issue on the radar at all?