I do something similar. Borg does incremental backups and snapshots.

Makes a snapshot so you can see how things where at X moment. The only new data are changes made since.

Then rclone copies that new data over

Borg does but if you sync with rclone you might end up uploading full data for every upload depending on the change of your data. This might be very costly and that's why they suggest a active host for backup.

Borg's dedup is more than incremental backups. It dedups blocks/areas even within the first run. No significant run of data is repeated with a single repository.

Yes, AFAIK it does.