The thing about Pokemon Trainer is that its design gave no choice
but to have a rock-paper-scissor element to the different Pokemon to justify them.
In fact, out of all the Pokemon characters in Smash, only 5 of them are starter Pokemon; Pikachu (Yellow only), Squirtle, Ivysaur, Charizard, Greninja.
Note how there are no Gen II or IV starters despite these generations having playable representation. Pichu for Gen II, Lucario for Gen IV.
Oh, and then there's the fact that Gen I had none of its original starters until Brawl. Instead, we got Puff.
Yes, starters are popular (which is normal since
everyone is gonna see them), but being a starter doesn't mean the character will instantly be in Smash.
Grass is weak to fire, which over half the Smash cast uses. Have fun.