Anybody remember this quote: "Strong Pokémon. Weak Pokémon. That is only the selfish perception of people. Truly skilled Trainers should try to win with the Pokémon they love best."
Typing does not define how good a pokemon is, it is how you use it that defines how good it is. Sure, it could have six weaknesses, but you're all assuming it will be a sweeper. It could very well be a supporter so it comse in, sets up Leech Seed or whatever and then leaves before much can happen or it could get a really good moveset which lessens the impact of the weakness like Pursuit so it can switch into something it is good against and when that pokemon is switched out use Pursuit, or Sucker Punch so it can get in a powerful hit before it gets hit. You never know...
Typing does not define how good a pokemon is, it is how you use it that defines how good it is. Sure, it could have six weaknesses, but you're all assuming it will be a sweeper. It could very well be a supporter so it comse in, sets up Leech Seed or whatever and then leaves before much can happen or it could get a really good moveset which lessens the impact of the weakness like Pursuit so it can switch into something it is good against and when that pokemon is switched out use Pursuit, or Sucker Punch so it can get in a powerful hit before it gets hit. You never know...