[WatchMeBeQuieter]

Gyarados and Charizard are both from gen 1. My theory is that the Dragon type was added late into development, as there are no damage-dealing moves of that type in gen 1, and only 3 Pokemon of the type. The best replacement of the type they could find was flying, which explains Gyarados, if not quite Charizard.

Then Dratini, Dragonair, and Dragonite, which appear late in the Pokedex, despite being able to be found before having 5 badges, were probably added late in the development to make one superpowerful non-legendary Pokemon with few weaknesses to be used by Lance.