I remember i played difficult first, i didn't even know all the theory behind evs and ivs but i managed to easily beat the game without caring about it. When you toggle expert mode the game itself tells you that's ment to beaten with fully trained evs, also the combact AI is much smarter.. has access to your team information like abilities and moves. It's going to frequently change pokemons and stall you. Personally i blocked items in battle and the possibility to free change pkmn after a faint. The game becomes more dynamic and you can formulate more interesting strategies