Sway does server-side decorations. It draws window borders and a title bar for you, and handles the drag events in the title bar and borders for you.
Go ahead and make a basic Wayland window in GNOME. Compare the user experience to KDE or Sway.
I believe you misread my comment; I said that the full-screen, minimize, re-size isn't part of the server-side decoration extension, but was part of a more basic xdg_shell protocol through the configure event.
I was objecting to the fact that you said that windows did not have this capability without the server-side extensions, whereas I think they can be through configure. I did not dispute whether sway had server-side decorations or not.
Possibly this is a subtle distinction, but I do think it matters.
[1] https://github.com/wayland-project/wayland-protocols/blob/ma...