I also use Synology, and love it. However, I never use the cloud for any data backup. That being said, if you want high availability of data, the cloud would be the answer. I can access my NAS/server in my basement from anywhere in the world. Have done so many times, using the local Wi-Fi access or cellphone hotspot for remote desktop or direct access. Routinely backup the NAS to a separate 8T drive.
All of my network back ups are saved to my Nas device. However, critical data such as photos, personal information, bank records, etc., are encrypted and backed up to one of several cloud providers. The data stored on my Nas is primarily virtual machine data to recover in the event of a ransomware attack or some type of unrecoverable data error on my network. Otherwise the stuff I truly cherish goes to the cloud somewhere for me.