The advantage depends on the number of people who wait until the days they want to open up. If 100 people wait until their dates open and we get a 7 day jump, then we/i get all the open sites...
I'll open my beach front camp site to those who want to stop by for a beer.

A 7 day advantage is better than none, the park does not control over the campsites the Govenment has a central system that handles all bookings for Wa & Or.
If you want to play you need to know the game. Ever wonder how grandma gets all the good sites, stop by with a bottle of wine and ask, or sit with the college summer hires and learn the game.