Nexus Blitz: The nexus is way too tanky in Sudden Death

We had about 15-20 seconds where we were wailing on the enemy nexus as 4 players when they weren't there yet, and barely dealt a quarter of it's health. Got wiped since we were 3 APs and one AD and the APs had all abilities on cooldown thinking we'd take down the nexus before the enemy got there, and the enemy team takes down our Nexus with the 1min death timers.

Don't really understand why sudden death should make the nexus that tanky.

Not to mention it really sucks that we spent a lot of power to win the last event and got cursed enemy minions when the sudden death was literally just starting. While normally a strong reward, it's just about worthless when the nexus walks out exposed.