And you know what? It really wasn’t.
Whedon thinks he has to kill off a main character to make the audience connect emotionally to the film. He overuses this trope so much, that it entirely lost it's intended shock value. He seems to fail to understand that there are things worse than death. I mean, look at CATWS - the most gut wrenching film in the MCU and no one dies there. On the other hand I couldn't care less about most of the new characters in AOU. I even predicted that it would be Pietro who dies. Main characters were (1/3)