In GNOME, terminals are not children of the window manager, or even of
the session manager. When you ask for a terminal, GNOME sends a letter
to dbus, asking dbus to please make a terminal. Your gnome-terminal
is a child of dbus, and inherits its environment from dbus.
You do not get full control over dbus. You can't tell it to set its
umask to 002, or to set one particular locale variable differently from
the rest, and so on. There's just a limited set of things you're allowed
to tell it to do, and good luck finding the documentation for those.
so in my terminal, I can see the parental relationship is,
init -> systemd --user -> gnome-terminal-server -> bash
where init is /usr/lib/systemd
how do these three processes fit into your dbus description?