redleader and Nigel Smith,
There surely can't be any Catalog updating in the run of a Copy script, because that script doesn't designate a Media Set as a destination—no Media Set means no designation of a Catalog. That's why I thought my test might run faster than the equivalent Recycle run of my Backup script. In fact its copying phase ran slower. Maybe cramming copies of multiple source files into a single .rdb file is faster than adding each copied file to the macOS HFS+ filesystem, but I'm not inclined to investigate it.
There weren't any files in the destination folder. I had deleted all those that were copied there by a test run I killed after 5 minutes, when I noticed the script mistakenly specified Copy all files (which wouldn't require name comparison) instead of Copy only missing files—which redleader specifies.
In any case, my test proves that redleader could get his backing up done faster with Backup scripts. He could also use the resultant Catalogs to do grooming as Nigel Smith suggested. I don't bother with grooming, since I must—because I've experienced multiple cases of water leaks from an apartment two floors above mine—swap a portable HDD containing complete-as-of-Friday-morning backups of all my drives off-site once a week.
P.S.: On pages 120–121 of the Retrospect Mac 16 User's Guide, under item 6. there are 5 paragraphs following this single-sentence paragraph:
that describe not only the pop-up that redleader shows he chose in the screenshot in this up-thread post, but each of the other pop-up options. Those 5 paragraphs have been deleted from page 110 of the Retrospect Mac 17 UG—evidently by the StorCentric Slasher (my name for him 🤣 ).