But IV's/EV'd are important, even in reborn. Not that you wont be able to beat the game without it, but if you want a smooth play you should at least reset/breed for decent IV's and at least EV train a little, change nature if it is bad for the pokemon (adamant Gardevoir). As an example, a untrained/0 IV attack/ negative attack nature lvl 100 Blaziken would have 220 attack, while a EV trained/31 IV attack/ +attack nature lvl 100 Blaziken would have 372 attack. That is a 152 point difference.