says who ? As much as I love marvel they take more liberties than DC to be honest and if your not in every marvel thread railing about it then let the creators tell the story they want and it fits the superman messiah narrative so I can't see your problem .If the traditional superman doesn't die, there is no actual depth to his death. He is just a strange alien man who died saving them like he did for about a year.
The power of Superman's death in the comics isn't because what it does for Clark Kent, its the effect it has on the entire Universe, specifically the people of Metropolis who have grown over years to love and respect Superman, the way he love them right back. Its why there is power when superman is paraded down the streets and has his funeral with the whole DC super hero squad coming, the statue for him, ad etc.
You kill his connection with the people, the city, the entire universe, you kill a "hero" who hates being a hero, who hates his life and has no purpose and it literally means nothing.
Dying to find oneself and to become a true hero is not a superman story and it just shown how Snyder never had a ounce of understanding for the property and that WB allowed him to start this nonsense is why the DCCU is in complete and total shambles from the ground up.
All this is my opinion though.
He didn't hate being a hero he was learning to be the superman you seem to want, a superman growing up in the world of today in which everyone has an opinion about everything and would be mistrustful of a godlike figure who appears to only want to do good for no apparent reward . People can't even agree if fluoride and eggs are good or bad and you think the world as a whole would just be like yesssss a superman !!Especially after all the destruction Zod caused . His death shows and reinforces that he is serious about being humanities protector to the doubters