>What got me off Facebook (>3y ago, not a passing whim) was the realisation that I found no value in keeping in touch with people I was only 'in touch with' via Facebook.

This. If you're only interested in keeping in touch with people as long as it takes zero effort on your part that means that you don't really want to stay in touch with said person. Once I realized that, being done with social media was easy. I run a nextcloud instance that allows me to share photos and large files with family, and anyone for that matter.