>>55508138That's the point. It's a knowledge check. You go up against Brock and you gotta know what rock is good against, what rock is bad against and guess what pokemon brock will most likely use. Also it doesnt really matter if you know the type advantage if your pokemon aren't strong enough yet.
Take Erika for example. You know she's a grass type trainer in Kanto. And for whatever reason you don't have a fire or flying type. You can infer that due to the amount of grass/poison types in Kanto that a really strong psychic pokemon would be able to deal with most of her pokemon. Or maybe you teach a pokemon a coverage move you wouldn't have otherwise. Or train up a fire type you neglected. Or make a team so strong type advantage doesn't matter.
Also isn't the league also just 90% people who focus on one type of pokemon? The only reason they mix it up in Kanto is cuz there's not enough ghost types for the ghost one, not enough ice types for the ice one and not enough dragons for the dragon one.