Yep, it is a load of crap to have to install a new wiring harness when it should be rigged already. How much is LR really saving by doing this? Unless it's a scheme to help the dealer sell accessories!!! At least for a hundred bucks you get a nice plug that handles the 7pin AND 4pin without needing to use an adapter(such as when equipped with a 7pin only and the trailer is a 4pin).
The wiring kit replaces some wiring and adds a bit more. Basically, the new harness goes inline with the lights, plus if you have the rear distance sensors, it taps into those. So if you have a trailer connected, the rear distance sensors actually get disabled which is quite nice. Not like you couldn't just press the P button when backing up!
What is nice is that if you have to add a brake controller, the connector is located up under the dash already. Just buy the controller, get an F-150(around year 2000+) plug, and slap it in! Some connectors actually state the F-150, plus now the LR3/RRS!