My vice guild master's equip is around +10 evil to +4 pegasus gear.
when i observed him fighting the summon gate i saw the magic damage, it was 90k
i think his HP
was around 100k since he survived with some hp.
it's just like any other ND, destroy the towers first, and then the gate's damage will be lowered.
its physical attack didn't hurt much, so Holy Guard your main char's line and it'll be safe (bring lots of ressurection scrolls).
btw most of the bosses & gate in Yggdrasil is flying, so bring your flying hitters (empress, sheriff etc).