Just for a point of reference, in the "Guide" section at the top of the site, there's frame data for most characters (All except Mu and Makoto). "Good" 5As, such as Bang's, Ragna's and a few others are 5 frames, the rest are 6. 5Bs are roughly 8 frames or longer. According to the Mu Guide topic, assuming I'm reading correctly, sword of decimation is -10 on block. So yeah, it's unsafe, but at the same time, ending a blockstring with a sword generally means they're going to be a decent distance from you. A few characters could probably punish it, but distance is just as much of a factor as frame disadvantage, so they'd need a really fast, looong reaching normal to do so. Personally I'd say keep at it until someone gives you a very good reason otherwise.
Jumpins: j.C and j.2C. Her other aerial attacks don't really stand out, so those two are your solid options. Personally I really love j.2C in general... Could just be me playing bad opponents but I can land silly j.2C shenanigans all day long
Antiair: 2C and 6A. 2C is excellent if you have the time to get it out, as it's a bit on the slow side, but it's air unblockable, and has a decent hitbox, easily comboed from, etc. 6A is your quicker option, but it hits more horizontally than vertically
I've been messing with Blessed Mirror a lot myself recently, and I've been fairly successful in using it as a sort of antiair and to punish a few things from a long distance. It can be comboed into, but I think the real beauty is the almost absurd damage it can do on its own as a punish