There is no need to spread FUD like that. Their “disaster waiting to happen” way of chunking and saving files is actually what makes it superior to Nextcloud for my and many other usecases. Without the active chunking while up- or downloading one needs to sync the whole file all over again if one bit changed. By chunking and indexing every file, you have the benefit of delta sync. On top of that you get versioning which ironically can be used as kind of a backup function on file level.

Besides that you can do proper backups of the Seafile data repositories and database for disaster recovery or use the FUSE mount for file backups.

I think the answer you are looking for is less privacy oriented than OP understands it to be. The benefit of renting computational resources someplace outside your control is e.g. that it allows you to send mails to known providers which otherwise would refuse your mail if you would sent them originatig from a private IP address or e.g. having a always on cloud storage without running a computer in your basement 24/7 etc.