Joomla native routing is not quite robust and you can't control how the SEF URL of menu item is built. You can only define menu item alias - a component of URL.
By default aliases of Joomla menu items are relative: aliases of all parent menu items are auto-prepended to SEF URL.
So child menu items have URLs like:
This plugin allows you to switch alias to 'direct' mode and have short URL without aliases of parent menu items:
Another option is not include alias of certain menu item into SEF URL of child items.
It would be much more userfriendly, if one could mark many menu items at once and make them "direct-aliased". It is pretty bunch of work, if one has many menu items - open, press button, save, open... It would be so fine and quick: in the menu items list: mark all up, press button "make checked direct-aliased" and you're done:)
This plugin is the answer. Its free, it took less than 5 mins to install and activate and it means I can have simple URLs like www..com/landingpage
It should also be cross posted in the Landing pages catgory of the JED.