If Cu first skill and second append skill are maxed, then double vitch is not locked by a mystic code too. So it's better, because you can use BG and any MC, while Cu+Vitch+Oberon needs a 50% charge CE.
Min neutral damage for level 70 Cu NP 5 10/10/10/-/10/- with level 100 MLB BG and artic MC and Double vitch: 86319/115837/174203