Use .php file as page instead of wordpress page & template file?

Yes you can do this but creating template like usercp.php .

 (1) First create usercp.php template and then this one line at first of template.

update_post_meta(get_the_ID(), ‘usercp’, 111);

 (2) Then create page and assign template.

 (2) Then go to your functions.php file and add this code

add_action('template_redirect', 'setPrivateTemplate');
function setPrivateTemplate()
{
    if (get_post_meta(get_the_ID(), 'usercp', true) === 111) {
       load_template(dirname(__FILE__) . '/your-folder-name-inside-theme/usercp.php');
       exit();
    }
}