I wonder if the setting concurrency-max-threads works on that. Release: 2.0.3.6 (canary) 2018-04-23
Actually that gives me an idea for another test for another issue =)
It by default uses many threads. I don’t think more or less thread use could be as easily identified through an assumption especially as backups change and as well as what’s done eg verification, deletion of old files, etc.