Yeah that's true, I do remember that Pikachu was a central character in the animes, which would obviously give him a lot of limelight.

But since the anime series started around two years after the first Pokémon games came out, I guess Pikachu indeed was "one in the bunch" during 1995 and 1996 and that most people back then thought of Bulbasaur, Charmander and Squirtle as "the main Pokémon characters".