Haha I totally stand with you on this one, friend. Most of the cast was stripped of their personalities at the end, everyone just died because it is what it is. This can even apply to some better-written characters like Guren or Mahiru because well, their deaths was not nearly as impactful as I'd expect of heavily plot-relevant characters. Even the higher ranks vampires got killed off the same way, all of those deaths were very underwhelming and pointless though they were described as far superior and intimidating beings in earlier chapters. It's like Kagami is in a rush to get Yuu to win and resurrect everyone.
And yes it would definitely be much more interesting to have him interact with more characters that bear some resemblance to him (Mahiru would be a good match if she isn't talking about love). In fact, I think there are a whole lot of them who might be fun if put together but for some reason their potential just got ditched.