Did you try out Nextcloud AIO instead of setting it up manually?
Yes, mostly the same.
I agree that NC has a lot of problems. It’s a good example of an application that tries to do everything and unsurprisingly doesn’t do many things truly well. With that said, I was surprised that NC AIO ran well for me despite the horror stories of NC I’d always read
I believe this is a problem of scale, once you get a lot of data and a couple of users things then to go downhill from there.
To make things better NC isn't polished at all and there's a lot of moving parts that break randomly at multiple times or at the same time.
My main problems with Syncthing is that there’s no official iOS client and that there’s no easy selective sync
This is kind of the problem with Syncthing for... everyone. What I do with iOS is to avoid syncs, have a central "server" where all your Syncthing devices sync to/from and access everything on iOS through WebDAV/SFTP or FileBrowser running on that server.