I can understand wanting a second team for when the content is stacked against your primary one, however I dont really see A. Yomi being capable of anything that your Gadius setup cant already do. It looks to be more of a sidegrade rather than something that's got some horsepower behind it that will help you get through some of the tougher stuff they've added since A. Yomi was new. That might not be the criteria you're using to decide on whether or not to build the team, but with the work involved if it wasn't a significant upgrade, it's not worth the resources imo.
I'd say we're around a week away from another godfest. Roll some if you can and if you are intent on a dark team, keep your fingers crossed for a Typhon or Gremory. Gremory is the dark heart cross leader (6* GFE) that runs off of Devils and Balanced types, and Typhon doubles as a great sub for her as well as a potential outstanding leader once the armors go in and you can change him into Anaphon (same heart-cross strength as Gremory but stat boosts!). Very strong leads, but it will take some luck to grab em.