I think they realise they got caught out. Alexandria Boss 1, for example, isn't split second reactions. It sets out the naughts and crosses way ahead of time and you can see what order they're gonna do. You have quite a bit of time to look at it and go "okay dodge, in, dodge, in". Then after its tutorialed you it adds in the front cleave or rear cleave attack to the mix and it still gives you a couple of seconds to figure that out.

Is it a bit more complex than normal? Yeah, sure, why not. Does it give you more than a split second to react? Hell yeah it does. Gives you loads of time. The level 100 Dungeons are only hard if you've spent the entire game relying on the orange no-no zones instead of looking at the animation telegraphs or unique attributes of certain attacks. Like circular sfx are generally going to be a donut and crosses are going to be explosions. You can never be hit by certain mobs, like the early games Cyclops, purely by looking at its animations rather than attack names.