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Unironically out of the gate I think Brock does an excellent job of forcing new players into learning the basics of the games. Doesn't matter which starter you chose, it immediately teaches the player "okay, type match ups are a thing and they matter, you can't just spam A and use tackle non-stop to win". On top of that, it also teaches kids who picked Charmander that "you need to have a diverse team of Pokemon to take on all challenges, you can't just use one Pokemon".
Obviously it's far from perfectly designed and people who choose Squirtle/Bulbasaur get a significantly easier fight than those who go with Charmander, but either way, think of all the dumb kids way back when who just spammed Tackle because it did damage and was at the top of the move list. It's a simple lesson, one that might boil down to just "press down twice before you choose an attack next time", but it's effective nonetheless.