One other nice thing with Resilio Sync is that it supports selective sync on an easy per-folder/file basis. While you can sort of do this with Syncthing by using ignore lists, it’s much easier with Resilio since you can just right-click/open files you want to keep on your device.
I have my storage mounted from my NAS using NFS and this is added to Nextcloud using the External Storage plugin. Works great.