Recently learned that Dalion had a total party wipe attack during an early phase
I fought Dalion plenty of times and have never ever seen that attack happen. Due to the chaos of public queue, I've learned to guard and parry against the elemental death balls thrown by the minions if left alone. It wasn't an issue for me, so I just accepted that getting sniped from across the map was a given and used it to my advantage. If those things are left alone for too long, they will summon an actual "you've met with a terrible fate" DEATH ball at the center of the stage that can kill most players once it explodes. I survived thanks to Tough Mind, but I know what I gotta do now.
Don't assume the group of 3~7 players will split up and fight other minions. Don't assume ranged players will close the gap to prevent more Death Balls. Suck it up and be the hero they need even if it means you gotta do it alone.
I'm not sure if it happens during the phase with 2 minions, but it definitely does during the phase with 4 minions.