My Diamond team, they went through torture, but they beat the E4.
Friend (Alakazam) lv 50
Dialga lv 47
Bronzong lv 35
Chatot lv 30
Abomonasnow lv 38
Steelix lv 43
and yes those were their levels after I beat the E4
they were really under leveled and you still beat the E4 wow
I used a ton of revives, I actually didnt do as bad as I thought, the only hard part was Cynthia's Milotic, I had my Abomonasnow left and used revives until it was left with struggle, then it fainted and I won, took a while but its possible.