ELI5: How are the current dungeons hard?

[Caitamm]

No it's not, because that's when the netcode limits starts to show. Which was exactly my initial point

I don't see how reaction time is factored in here. You know the exact pattern of X/Os well before the first one even goes off, you know the order they are going off in. Additionally, you know the pacing of when the damage comes out unless it's your very first time seeing the boss.