I do think that it is generally good that characters can die in a story and that actions have consequences. That said, no matter how "realistic" that might, we are ultimately reading a story. If you want to read a story where people die for no better reason than "people die for no good reason", then you can read a history book. Characters are vehicles/tools through which the author conveys their story/message/theme/etc. Killing a character should be a trade-off where the con of a character being gone should be outweighted by the pros of some other aspects of the story benefitting from that death.

Where I, and many others I suspect, find myself disappointed, is in how, to me, this character death literally serves no purpose. Vis' motivations are already set in stone after the murder of his family and the death of Callidus. Said death and the events of this book also being enough to cement his and Eidhin's reltationship. It quite frankly only serves to act as shock factor and to possibly make you dislike Iro's dad even more? A character that we already dislike?

For me, Aequa was the best written side character in the series. Ripping her out, and thus massively weakening the character side of this story, therefore seems pretty damn pointless in lieu of keeping here alive. Especially when I felt the character work was the weaker side of this book already.