Rclone local repository (linking to post from rclone backend author) would be worth a try to see if:
Adding Rclone as backend #2957
Provides a backend to rclone, allowing to link multiple cloud storage providers and technologies.
will achieve more or less the original goal. Specifically, for you, I see these rclone storage systems:
and perhaps you or someone can also try:
and if they work, maybe spread the word…
Choosing sizes in Duplicati may help if performance suffers from small file transfers through rclone, which isn’t doing its usual thing but is started for each file operation. That restart might add a delay.
On the other hand, slower operations are probably better than what Yandex WebDAV is doing now.