I feel this episode was kind of weak for a finale. Mana was introduced but she never shows up again, she didn't even get her second scene, and both Ruby and Kana's high points felt very short. It feels like they decided to set up season 2 more than actually wrapping up the season. Still a good episode but lacking for a finale.
Yeah it doesn't even feel like a finale. To be fair it is just ending 1/3 into the manga so that was never really meant as a stopping point. It's probably pretty difficult to turn that into an ending while staying true to the source.
Watching it weekly this kinda sucks but I have a feeling in hindsight once the other seasons are out it will be extremely bingable, just like the manga is.