Do you think webdav somehow dumps you database? No it’s just a protocol to save your files on your webserver. It’s just a middelman.
Umn. It allows the application to do its own synchronization and diff resolution. It's why they recommend it.
Directory synchronization is a "best effort" to copy files back and forth without considering the application's needs. Copying database files while they're being written can be problematic for example.
Both Nextcloud and syncthing will synchronize a folder. And it will probably work if you aren't making lots of changes on both systems. But there is increased risk.
Yeah it’s my recommendation from my personal experience. Is that wrong?
Yes - absolutely. "I've been lucky so far" and recommending against what the product you're using says you should do is TERRIBLE advice.
The point is, syncthing is rock solid, never had any issue being it with my zotero database or syncing files between my devices. If you’re a Nextcloud advocate or are against my personal opinion so be it :).
Why are you getting defensive towards syncthing? It seems fine. It's the wrong tool for what you're using it for.