>>38017688Dragon had a wildly different design philosophy in Gen 1 than it did for Gen 3 onward.
Dragon more or less literally only existed for Gen 1 so the penultimate boss, Lance, could pull out a Special Snowflake Type that resists all of the Starter's Primary Types and was exceedingly rare.
They still wanted to uphold that idea for Gen 2 but also give Clair her own Special Snowflake Combo (a Dragon that can't feasibly be harmed Super Effectively without grinding for Outrage Dragonite or trading shit) which is why Kingdra is the sole new Dragon of Gen 2, and also why Lance doesn't use one because that'd take away from Clair's Snowflake Factor.
It wasn't until Gen 3 that they started phasing Dragon out from this philosophy and just made it an uncommon typing to see outside of Legendaries.