I did actually notice the ZFS gui which is indeed something lacking in proxmox which doesn't default to ZFS in the installer. However once you do install it using ZFS it actually makes use of it pretty well and the user does not need to mess with the zfs cli tools much. Obviously it would be nice to have a GUI for all zfs operations too. Then again even TrueNAS refers you back to the cli for SOME operations.

On proxmox ZFS syncs do not require proxmox backup server, which actually has its own format which is very efficient in speed and disk space, but you do either need something like sanoid/syncoid or use of the shell.