^Well, originally the Dragon Pokemon were created to be some of the best in the game. They're slowly straying away from that now, with things like Altaria though.
One reason why there were so many Water types was because in RSE, it was about Groudon and Kyogre. That's why, if you look, half of Hoenn was water, and the other half was land. They needed to represent the fight between the legendaries. And, if half the map is made of water, it'd be silly if 1/17 Pokemon were Water-types. We should consider ourselves lucky they didn't make it 50 sea Pokemon : 50 land Pokemon for RSE (although that would've made those excessive sea routes more interesting.
This is a Total of 712 Types shared between each Pokémon.
Now, the problem is with this is some types are being very neglected. Does anyone know why there are so may Normal and Water types compared to Fire and Rock types?
Wh does no one care about fighting types? The majority of them came in 1st gen anyway. Ghost types should be boosted. (Name 1 ghost type legend). There should be more Dragons too. (Again, name a Dragon legend besides Lati@s (Not one in most people's eyes anyway) or Rayquaza). Dark/Ice types are very neglected too. We need more.
Personally I think that Gamefreak should make more dragon/ghost types since they're a lot of people's favorite type.
And they'll hate it. Gamefreak's done it with Blaziken and Infernape, and now look at half the forums.