I know exactly how Synching works, the point is not the p2p nature of it, the point is that Nextcloud's sync performance and reliability isn't even comparable because the desktop clients, sync algorithm and server side tech (PHP) won't ever be as performant at dealing with files as Go is.

The way Nextcloud implemented sync is totally their decision and fault. Syncthing can be used in a more "client > server" architecture and there are professional deployments of that provided by Kastelo for enterprise customers with SSO integrations, web interfaces, user management and whatnot.

Nextcloud could've just implemented all their web UI and then rely on the Syncthing code for the desktop / mobile clients sync. Without even changing Syncthing's code, one way to achieve this would be launch a single Syncthing instance per NC user and then build a GUI around that that would communicate with the NC API do handle key exchanges with the core Syncthing process. Then add a few share options in the context menu and done.

This situation illustrates very clearly the issue with Nextcloud development and their decisions - they could've just leveraged the great engine that Syncthing has a backend for sync but instead, as stubborn as they are, they came up with an half assed-solution that in true Nextcloud fashion never delivers as promised.