People who say that it's weak might be dumb. Swampert is fine.
Tested Swampert 130 against wild: Charizard 130, Golem 130, Steelix 130, Electabuzz 130, Arcanine 130, Blaziken 130 and Elder Charizard 130. He killed all of those Pokemons except Elder Charizard.
As a Pokemon Swampert is fine, it only has ground moves that does not affect Charizard, so that's why it's kinda weak against him than other water type Pokemons who has more water type moves or other type moves that affect Charizard 1/2x, x1, etc. People should learn the dual types of each Pokemon first and then they can say what they want. I'm kinda out of patience because of that.