Even though Avengers: Endgame has been out for around two years, fans are still having passionate discussions about it. The film was received well by fans and works on many levels, and was an unforgettable cinematic experience, but that doesn't mean it's exempt from criticism. Some of the writing choices that were made are things that haven't sat well with fans over the past few years.
One of the most prominent of these is the way that Captain America ostensibly leaves the MCU. He takes the Infinity Stones back to their proper places in time and space, and then uses that time travel ability to go back and live out the rest of his days with Peggy Carter. Some saw this as a sweet and fitting end for the character, but a large group of fans don't like that this ending goes against Steve's entire character arc over his time in the MCU. Marvel needed a way to get Chris Evans out of the MCU because his contract was up and he wanted to step away, but there was a better way to do it: killing Captain America off in Endgame instead of Tony Stark.
Steve dying in Endgame instead of Tony makes more sense on a lot of levels. Killing off both would have been too much, especially after losing Black Widow earlier in the film. Tony making the sacrifice play does make sense for his character arc, but it's an arc he's already had in The Avengers. In that movie, he sacrifices himself and guides the missile into the wormhole so that it doesn't hit New York (it ends up working out fine for him, but the intention was there). Having him sacrifice his life for the world yet again just feels a bit redundant, especially when a lot of his arc in Endgame is about how he wants to keep his family together. Of course, Steve Rogers also sacrificed his life for the cause in Captain America: The First Avenger, so he's no stranger to this either, but it makes more sense for his arc in Endgame specifically.
In general, Steve as a character feels like he's completed his story by the end of Endgame, but sending him back to Peggy goes against all of the character-building he's had in the MCU so far. His whole story is about learning to move on from the past and learning to find his place in the present...and he does. His ending in Endgame is a regression of all that character work and feels like lazy writing for the sake of giving him some white picket fence happy ending. If anything, the man who already had a family in Endgame (Tony) should have been the one to get that ending. If the big reason for Clint not dying on Vormir was because he had a family, why wasn't Tony afforded that same luxury?
Steve still would have had a very emotional death scene, and it still would have felt like a massive loss. Iron Man may have been the first movie in the MCU, but Captain America was "the first Avenger," so he's just as integral to this universe as Tony Stark is. He could have had a similar scene of his friends - his found family - all around him as he died. Obviously, Sam and Bucky would have been right there with him, and we could have even gotten a very emotional callback to the "I'm with you 'til the end of the line" quote from Captain America: The Winter Soldier, as it really would have been the end of the line for Cap and Bucky.
On that note, if the MCU was looking towards the future, Steve dying in Endgame would have made The Falcon and The Winter Soldier that much more emotionally loaded. Instead of Steve giving the shield to Sam in person, perhaps he left it in his will that Sam would be the one to take the shield. The show as it is currently has a focus on Sam and Bucky wanting to protect and uphold Steve's legacy, but that would have felt a lot more poignant if Steve was actually dead, rather than just...time traveling. It would have made John Walker's take on the Captain America persona a lot more offensive to Sam and Bucky as well. These two characters mourning their dead best friend has a lot more emotional weight than just them feeling a little sad because he left.
Of course, the decision to not kill Tony Stark would have had other repercussions in the MCU, but most of them might have been for the best. Spider-Man: Far From Home would have had to be tweaked significantly, but it might have given them a chance to let Peter Parker have his own story that doesn't revolve around Tony Stark and the messes he created. Tony wouldn't even have to be all that involved in the next phases of the MCU at all; they could have written it so that he took a sort of retirement to just be with his family and stay away from superhero problems, which is believable after how he spent the five years after the blip. It would have also allowed for Tony to come back sporadically in the future if it fit the story, however, because it seems as though Robert Downey Jr. was less ready to give up the MCU than Chris Evans was, though no one really knows for sure.
Even big fans of Steve Rogers seem to agree that killing him off in Endgame would have been a better move than killing off Iron Man and sending Steve to a fate that doesn't fit his character arc (not to mention the fact that it undercuts the arc that Peggy experiences in Agent Carter as well). It will be interesting to see if Marvel did this to keep open the possibility that Cap could come back one day, or if the character is well and truly gone for good, and was given the boot in the most boring way possible.