I give up. I can't even beat H Korrina with pubs because nobody but me is bringing Blaine. Does anyone want to help? I don't have Hilda, I'm using the two Hilda guide from Gamepress so I guess it works the same for Hard:
https://gamepress.gg/pokemonmasters/story-battle-guide/battle-guide-ex-challenge-korrina-very-hard#sunny