@kev to add a data point I've been using mextcloud exclusively for file syncing and have been happy with it. I have everything on AWS and the files are stored in EFS + AWS Backup, and was actually surprised how smooth it all was to setup.
Only complaint is thumbnail generation slows my server to a halt, so I had to manually setup a plugin and cron to run that overnight. If I was less cheap this could also be fixed by upgrading EC2.
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