The idea of Shadow weaver corrupting Scorpia is pretty chilling but like you said I think she'd find it impossible. Scorpia would just get nervous and go on a tangent every time.
What do you think Bow would be like in an AU where he was in the same position as Scorpia?
OMG That's such an amazing concept. Bow and Scorpia are pretty similar in their roles as the friendship person, but the big difference is how Bow stands up to Glimmer in a way Scorpia doesn't do to Catra (to be fair - Catra would NOT have made it easy).
Bow also has a strong ethical pathos. In the show, his family told him to stay out of the war, but he joined anyway - both for the sake of his own identity and search for adventure, and to do the right thing. In the Horde I imagine he would do pretty much the same thing. Do what he was told, keep up appearance, but in secret be more and more worried about the Horde's real agenda (just like in the show trying to live a double life).
There are multiple ways to spin it. Me, I would have the first breaking point be adora's disappearance. Bow would learn from Catra and others that apparently adora thought the Horde was kinda, sorta... evil? He would not do an adora and step in front of a tank, but he might start to undermine Horde missions in secret. 'Oh no, the civilians got away. Someone must have warned them. Who was that mysterious masked man with a bow?'
The next big breaking point would be princess prom. I imagine him to be a princess in this au, so he would get the invite. He and Catra would go, she would be in charge of distracting adora and he would be in charge blowing up the place and stealing the sword.
and everything would work according to plan, until the big dance. Catra keeps adora agitated. Bow prepares to sneak away to set the thermal charges.
and then
the crowd part
and he sees her
Sparkly
Dressed in pink and purple
The most beautiful girl he'd ever seen
Giving him a most disgruntled look. 'I see you' she gestures.
With a stomach full of butterflies he still manages to set the charges, but Glimmer doesn't leave him alone. He manages to knock her out, and together with Catra they return to the Fright Zone with the sword and the kidnapped Glimmer. She wakes up in a cell, and he manages to trade a few words with her before Shadow Weaver whisks her away for torture.
"How can you betray the princesses like this?" she snarls through the bars. "You are one of us."
That shakes him in the core.
Shadow Weaver always told him the other princesses would hate him. That they turned against his family. That he wasn't welcome there.
He mumbles something about the Horde having to stand up to the evil princesses. He knows it's a lie.
"Like you did in Thaymor?" she asks and years of indoctrination and propaganda crumbles to dust.
Either he flees together with Glimmer and adora, or he stays a little longer so he can be part of Super Pal Trio with Catra and Entrapta. If he stays, i'd say he runs away a bit before Shadow Weaver. That means poor Catra is hit extra hard by the tripple betrayal of Bow and Shadow Weaver abandoning her, and Entrapta 'stealing her spot' with Hordak.
Bow is welcomed in Bright Moon and Catra is sent alone to Crimson Waste to die. She returns in a terrible mood with her own mooks, adora, the sword and no one to hold her back when she demands Hordak to open the portal now.
That's my take, but there are plenty of things one can do with it. Maybe most interesting would be Bow having a "Scarlet Pimpernel" phase while staying with the Horde and in secret helping the princesses. There's a lot of fun Glimbow aspects one could take from there.
