The reason for the discrepancy is that on Murena the Gallery is more clever in collecting the “date taken” from the image.
Where you see photos “bunched” on the phone, the Gallery is using “Date modified”. It is typical of the copy command that the copies have their “creation” at that modified date.
Example keywords in possible correction is EXIF metadata.
Rather than copy a command like sync will more likely retain the real creation date.