I found some supporting evidence from bulbapedia "Clefairy was originally going to be the official mascot of Pokémon, but Pikachu was used instead due to the popularity of the anime and Pikachu's familiarity with fans".

Source: https://m.bulbapedia.bulbagarden.net/wiki/Clefairy_(Pok%C3%A...

Very cool find about the pink version!