I cheesed only 3 boss battles. Flying gym type i used Feraligatr with sheer force, 6x dragon dance and one shot everything. Same thing for one rift pokemon. Also Madame X battle with revive spam (but you have to cheese her in every single mode if you want to win). It is hard, yes, but with good pokemons, good training and knowledge of enemy pokemons its possible. And yea, im not using set battle mode.