Gl-UI V4.0 already uses /etc/config/firewall to configure firewall rules. You can try to configure firewall rules in GL-UI and it will display correctly in Luci.
Rules in Luci are not fully displayed in GL-UI because of simple filtering in GL-UI. You can easily see that GL-UI only displays rules with name GL-*. Rules in Luci are complex and fully displayed in GL-UI would be redundant.