It's not like they are really single-type anyways, aside from Wallace. Lance had non-Dragon types, Steven had non-Steel types, and Iris had non-Dragon types.
Also, they all cover their type's weakness:
Lance-Dragon types are weak to Ice and Dragon. He has a Rock, a Fire, and three Dragon types(One of which has a Fire move). As for the additional weakness of Rock, he has a Water type. Overall, he has 10 types covered when it comes to attacks, giving him plenty to work with and counter a bunch of types.
Steven-Steel types are weak to Fire, Ground, and Fighting. He has three Rock types to cover Fire weakness(One is also part Steel) as well as a Ground type, two of his Pokemon are part Psychic(Only one has a Psychic move that can cause damage though), more over, most of his Pokemon take neutral damage to Fighting types due to their second type(Only two of his Pokemon are weak to Fighting types as well as half of his team takes neutral damage to Fire types due to one of their types. He has counters to Ground type as well. Overall, he has 11 types covered when it comes to attacks, giving him plenty to work with and counter a bunch of types.
Wallace-Water types are weak to Grass and Electric. His Ludicolo takes neutral damage to both Water type's weakness. He has a part Flying type(Which doesn't have Flying type moves, but it takes neutral damage to Grass, albeit it takes 4x the damage to Electric, however it has a Ground type move). One of his Pokemon is part Ground, and while that means 4x against Grass it also means immunity to Electric and it has a Ground type move. Three of his Pokemon have an Ice move. He only has 6 types covered when it comes to attacks, but of those types he has something to deal with Water type's weakness.
Iris-Again, Dragon types weak to Ice and Dragon. She has 10 types covered for attacks, of which she has moves covering her weakness. She has three Dragon types, of which two have moves that cover both it's weakness, and another covers it's Dragon weakness. And even without Challenge Mode, two of her Pokemon have items, a Life Orb, and a Focus Slash(Of which is held by Haxorus who has Dragon Dance). Overall, just like the others, she covers her weakness.
I prefer to battle champions that aren't type specialist, but from what we have gotten from them thus far is perfectly fine as they aren't completely single type(Besides Wallace) and they all cover their type's weaknesses they specialize in.
So no, I don't hate them. They can be plenty challenging with or without using types that are strong against their specialized typed.
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