There's not a lot of change between Ponyta and Rapidash, or Growlithe and Arcanine, or Seel and Dewgong, or Omanyte and Omastar, or Kadabra and Alakazam, or Pidgey, Pidgeotto, and Pidgeot, or Clefairy and Clefable, or Poliwag, Poliwhirl and Poliwrath, or Machop, Machoke and Machamp, etc.
I think less that all the Pokémon in gen 4 are terrible than I used to... but I still think a lot of them are over-designed. Gen 5 stepped back on that a little but there's still room.