I did my first brandish at 99 mage, 70 defence but I honestly think the only problem I had was not having super antis then. Got it done on 4th try! Wasn't too bad, you should probably keep trying.
The best way is to magic/ ranged. Have the brandish item in your action bar. Make sure you have a familiar full of food and that you use super/ extreme/ ovls. Vampyrism Aura/ SS helps a lot too.