WorstGen don’t know how to analyse the story. Ace dying is not meant to be just a feeling of absolute hopelessness for Luffy but for the entire world.
Ace was supposed to be the man that Whitebeard thought would bring the dawn. He put his faith in him.
I agree on the Sabo part though but we just have to accept that Oda doesn’t want this to be a tragic sad story in anyway