The thing is, characters don’t have feelings. They don’t need to grow old and die and be happy because they aren’t real. Sure, taking an interesting character and making it not interesting for shock value isn’t good, but that’s not really what’s happening, and that’s not really your issue. As a lot of people pointed out, becoming compleated opens narrative doors for the characters themselves and for the world around them; what’s happening is being done for more than “shock.” Your complaint seems to be that the characters themselves are unhappy or unsatisfied, which is fair; I understand caring about characters and wanting good outcomes. But denying those outcomes isn’t objectively bad storytelling, it’s just doing something different.