If the heroes are up against the big bad villain, the allies with intel on him are their most important assets.
Avengers: Infinity War – big bad villain is Thanos
The MOST IMPORTANT characters for our heroes’ victory, therefore, SHOULD be Gamora, Nebula, and Loki.
Loki dies in the first 5 minutes of the film to fuel manpain for a man who has already been in pain, Gamora dies to show gross “manpain” of her abuser/kidnapper/killer, and Nebula is shown for only two minutes being totured by said abuser.
Without these important characters, the remaining heroes are never able to properly, knowingly, fight against Thanos. All they’re able to do is react to the attacks from Thanos as they occur.
Like, I understand that a proper story needs to get to that point where everything seems to be lost, the eleventh hour where the characters are in the direst of straits, before the eventual victory. But if all the characters with intel on the villain need to be killed off or incapacitated, so that the rest of the characters just run around reacting instead of planning, in order for the villain to get to that point of apparent victory, then that whole conflict is just cheapened.
It’s the heroes deliberately being debased by the writers so the villain can reach that point of success.