Pros and Cons of the Pokémon Trainer?

[RoxasXIII]

How does Charizard have bad defense and Squirtle have good defense?
And Charizard is slow and strong

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I'm just trying to throw out an idea that would make all three of them equal. Squirtle has high defense cuz he has a protective shell, can use withdraw, and is a frickin turtle, known for their protective shells. if you remember the first pokemon movie, when ash's charizard fought with the charizard clone, ash's strategy was to win using speed rather than strength.
i just put his defense low so that he wouldn't be completely superior compared to squirtle and ivysaur.