It seems like every network filesystem is irredeemably terrible. SMB and NFS the stuff of security nightmares, chatty performance issues, and awkward user id mapping. WebDAV is a joke. SSHFS is slow. You can get really crazy with CephFS or GlusterFS, and for all that complexity, you don't get much farther way from SMB/NFS issues with those either.
My solution: Share nothing and use rsync.
Well one problem is that filesystem in general is a terrible abstraction both in terms of usability and in terms of not fitting well with how you design network applications.
I’d say Dropbox et all is closer to a good design but their backend is insanely crazy optimized to make it work and proprietary. There’s an added challenge that everything these days is behind a NAT so you usually end up needing to have a central rendezvous server where nodes can find each other.
Since you’re looking at rsync where you want something closer to Dropbox, I’d say look at syncthing. It’s designed in a way to make personal file sharing secure.
Samba is a complicated piece of software built around protocols from the 90s. It’s designed around the old idea of physical network security where it’s isolated on a LAN and has a long long history of serious critical security vulnerabilities (eg here’s an RCE from this month https://cybersecuritynews.com/critical-samba-rce-vulnerabili...).