Ace's death was shocking to readers, but not in the same way as the death of some flashback characters. We readers didn't have much time to bond with Ace; some were fans of him, but I remember a lot even mocking him for dying because of his own stupidity.
Ace's death is a good thing for almost everyone. Those who hate Ace want he dead, he is dead, pefect. Ace's fans crying over Ace's death, serving Oda's dramatic purpose, perfect. Those who don't like nor hate him, didn't think Ace would die, they were surpised; good plot. And Ace's death serve other purposes, like an important step for Luffy to grow up or something, etc.
I dare to say that Whitebeard's death was more shocking and emotional (to us readers) than Ace's, because the war made a lot of us like and admire the old man.
Almost everyone know WB was going to die. Nothing shocking. Just epic.
@Deicide:
I think this flashback will have a sad ending because I think we will feel Luffy's depression and later his acceptance.
IMO, for Luffy's reckovery to be powerful, we will first experience his sadness,
Oda may want a sad end to this flashback in order to enhance our understanding of Luffy's suffering
We already feel Luffy's depression.
So if your father dies in your hand, you will go remember what happen when your mother died?
Yeah yeah yeah the readers already pretty much feel the sadness, now let me awesomely build up an awesome character and then kill him off just to make them feel even sadder and sadder and sadder and tear their feeling apart yeah yeah yeah.
That death is cheap. Serving the sole purpose of making readers cry.
Belemere, Tom, Hiruluk, Saul,etc played super important roles in character development for the Straw hat. And you are saying Sabo needs to die just to make us and Luffy feel even sadder. And then something else makes him stop being sad.
Luffy doesn't need Sabo's sad death. He needs something optimistic to gain the strength to recover and look forward the future. If Sabo is not that thing and he is already dead, then he plays absolute no role in the story other than gaining some tears from hardcore fans, which is cheeeeeeeeeaaaaaaaapppp!!!!!!!!
If you want drama go watch cheap films that try to make audiences cry at any cost, which is as many as salt in desert.
And I think that, if Sabo dies, Oda will do it in a way that you'll like it.
You. Feel free to enjoy cheap films. I can't.