Lack of justification? The Symphogear wielders are the only thing standing between the villains and the Earth getting blown up in most cases o.o I'm really not sure what's particularly contrived about it, though GX's biggest downfall was its writing, I'll admit that much.
Regardless, you'll probably be glad to know that AXZ and XV are the best the series has literally ever been. The writing is similar, yet different, with a lot of focus on tying past events together and just doing a whole lot of neat stuff. They also realized basically all of their past mistakes and either didn't repeat them, or literally went out of their way to fix some iffy stuff. Not to mention that AXZ and XV were announced at the same time, so the story for those two is particularly well done since it was planned 2 seasons in advance. So you shouldn't have any issues with AXZ or XV.
As for hype? Yeah Symphogear literally always one-ups itself, basically without fail. XV is chilling at 8.37 on MAL right now, placing it at the 5th most popular airing show this season. Which is insane lol. AXZ doesn't pull any punches either, it was just damn good. A lot of people describe AXZ as "GX but actually good." As well, AXZ has far better animation than GX does, while XV is just absolutely phenomenal.
Like look at this animation:
https://www.sakugabooru.com/post/show/82691