I wouldn't say that. The ending was a tad rushed but it had a whole volume for that. I just wish they addressed a bit more stuff.
The manga was already zany and not really serious as you can see Lian and Lava doing whatever they want in prison without Tarja, Ono or anyone keeping an eye on them when they are the most dangerous inmates there.
Maybe I would like a spin off since this universe of heroes and villains is interesting and the author is pretty good at character designs.
Not sure if they are real siblings (similar eyebrows but one with green hair and the other with red hair) or childhood friends and Shu just "replaced" Alissa. As for the other part:
You'll see...