folder juggling will not help. The native Gallery app uses modification date, not the exif date, this thread describes it too: I found a gallery app that organises photos by Exif dates! - the gist is, use Fossify or Aves that both offer sort by exif. I hope the native app will at some point introduce a switch for DCIM (or any folder) to use date taken.
If you're a tinkerer..
this app (download linked debug apk) can overwrite mtime with exif data. It needs custom exiftool flags: -overwrite_original "-FileModifyDate<CreateDate" or "-FileModifyDate<DateTimeOriginal" depending where the app did store the date taken. It can also readout the filename itself if exif fails. Caveat: it worked for me on individual files, but not folders
On a final note: why did your FP3 get no updates? it has A15 available. Worst case, a sideload away.