Just to be clear... you currently have 500GB on your SSID on a MBA.
Either way, definitely use iCloud to back you device up and stop wasting time with the local backups.
House fires, hurricanes, theft, ect takes the device and the local backup way more often than the rare chance of SSD failure. In the event of a catastrophe, purchasing a new mac and logging in with your AppleID and having everything come back is amazing, magical even. Freaking out about finding your portable drive to take with you during an emergency is not a fun exercise.
Thinking about this in terms of loss vs effort: 1T iCloud is about $120US / year... if the data is THAT important $120 is an insignificant amount for peace of mind. If you are only currently needing to backup about 200G then you can get it for about half. A 1T portable ( which can be easily lost, damaged, stolen ) cost about $60US.