In order to be able to select a component and drag and drop it, the component must have a dialog.
Components do not have to be under parsys/grid/responsive, whenever you are creating a template, you can put a component outside of a parsys or a layout container.
"but already authored components under root is not showing up in page." - do you see any error in a log or in browser's dev tool? Do components have some dependencies (a core/proxy component, a sling model etc) that are not deployed yet and hence it causes a rendition failure?