It s almost that
Urbackup has a slightly different meaning for “incrementals into infinity” , if you use btrfs, it is actually capable of using reflink for incrementals. This store only the differences between files. it copie the file in reflink mode, this takes zero space. Then tell it that only some chunks have been modified, and only theses chunks takes more spaces.
urbackup can do something like link dest for identical files in rsync. But not only for a file that s in the same place, it can also link a file which was backuped from a different server or from another place on the same client (my undertsandiung is that database is required here)
All this doesn’t come for free ressource wise. This is why you have some kind of slider that you can set in advanced parameter: transfert using raw, hashes, chunk hashes. This is because raw use no extra cpu compared to rsync, hashes allow to track fully identical files, chunk hash , allow to track partially identical files. So this slider change the cpu/bandwith balance and is tunable for full/inc local/wan file/image.