You can do far worse than Rebel Captive.
I think Sabbac with Optimised is nice. His extra, largely unmodified dice work well with Krennic's ability and the bonus shield helps him avoid damage long enough to roll them. Krennic's free locks boost up Vermeil (whatever upgrade you give them it's important to have the prototype fire before krennic's ride).
Duchess....is an excellent dogfighter for her points. Against other arc-restricted ships, she shines. Against turrets, she's pretty weak.
I would strongly, strongly recommend getting her veteran instincts if you field her at all, though. Her ability to take Veteran Instincts without compromising her free reposition is her biggest strength, letting her outfly Fenn Rau, Soontir, Adaptability Poe Dameron, and all the other scary PS9 ships out there.
If you wanted to drop Lightweight Frame off Vermeil, don't forget Multispectral Camo; it's only a point, but it can really mess with opponent's choices because they have to factor in the 1/3 risk of their target lock fizzling as soon as they apply it. Paired with Rebel Captive whomping Expertise, and it can make Vermeil an incredibly unpleasant target choice, even if he's jamming someone else...