Actually you only choose one of the main D/P/PT mascots and depending on what version you can get either Kyogre or Groudon. So in fact , you can get only seven without Rayquaza. Anyways , Rayquaza really is just an extra because you need to get the Legend from the opposite game , so if you buy HG and get Kyogre , then you only need to get Groudon and vice versa.
HG/SS has actually 8 available legendary pokemon including the Version mascots ,the 3 legendary cats ,the 3 ancients ,and one of the D/P/Pt mascots you get from Arceus. So actually HS/SS has the least legendaries of this generation of a main game.