Gigglestomp what are you talking about? Where was an Archangel on that list?
Ferrovax was clearly scared of her, Vadderung too. Notice they didn't even attempt to protect or defend Mab? Also the reactions both of them have...are both terrified and both sound like they are being forced/compelled to talk. Note the gasping?
What makes you think that was Ethniu's "true form" anyhow? Not to mention she remembers what One-Eye once was and that he is now almost mortal. Where would you place her now? She respected Vadderung when he was Odin, or whatever he was once. Not what he is now.
Reality did have trouble with her. Dresden could barely keep his thoughts together, he started moaning and worshiping. All the mortals did. Reality couldn't even contain her speed or power. Dresden had to work out her attack by inference.
The surrender Reality thing was if Mab isn't there to defend the Gates with her army, then the Outsiders get in. It wouldn't be instantaneous. An army without it's leader is weak, and Mab is their strength.
Ferrovax talks about cracking the gathering of monkey houses, which Jim says is more like the world bending around Neo than literally cracking the earth. That said, Ferro does talk about how his contribution to the fight if all out would do more damage than good - by which he is implying colateral damage. He isn't discussing what would happen to reality, but to Chicago itself. But that isn't to say he is anything on Ethniu's level.
The beings on the list were (not including the nations): The Mothers (who wouldn't), Titania (exactly 50/50), Ferrovax (stronger in a slugfest, Mab would be loathe to take him head on), Drakul, Cowl (if he completed the Darkhallow) - he would have become a minor God. Which all assumes Mab is alone without her army outside Faerie...just like she was in Peace Talks.
The Archangel's are not on it for another reason - they don't act because they can't, apparently. But tbh they are all on another scale entirely.
Ethniu is a God. A Titan. She might not be the strongest, but she is the last and she has gone mad. If the others were capable of beating her, they would have shown up.
Cowl would have been a god, Ethniu is a god already. Either way, both could have beaten Mab who is merely a demigod. A God trumps a demigod, in raw power.
But if you want to talk strategy, allies, options and favors...well that's a different story.