I’m currently testing it on multisite and it seems to be working; network activated with sub-folder install and domain mapping.
The visual composer menu item is not a standard menu item…
adding the following to your functions.php will hide it:
function custom_menu_page_removing() {
remove_menu_page('vc-welcome');
}
add_action( 'admin_init', 'custom_menu_page_removing' );