That’s quite interesting. You might want to expand into some other backup programs to add value to the backup comparison:
(a) Borg / Duplicati: These do consolidation of data-chunks into 500Mb (Borg) / 50Mb (Duplicati) blobs which may show interesting results for the small file test you did.
(b) Duplicacy - The dedup of Restic doesn’t deal well with changes that shift the chunk boundaries (see some work I did in link below). Duplicacy is much better in that respective (and generally a strong performer; does lock-free like kopia). Worth to have a look and compare as well.