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As much as I like using Starmie competitively, using it ingame turns it into brainless and wholly unenjoyable experience because of how absurdly broken it is.
>so fast nothing will ever outspeed you without priority
>acceptable bulk to tank at least one supereffective hit
>acceptable attack stats + Water/Psychic STAB + BoltBeam coverage = everything dies in two hits at worst
Improved Bug, Ghost and Dark mons make it less absurd in later generations, but nothing you can't manage with slight overleveling and EV gains. I once tried to solo the game with Staryu starter and gave up before third gym when I realised there's zero challenge waiting for me.
Pic related: hardest RBY and FRLG fight, for a very good reason.