The conclusion to Avengers: Endgame saw Captain America's partner Falcon taking up the shield, and likely the mantle that Steve Rogers had held since World War II. This isn't unprecedented or surprising, since Sam Wilson also picked up Captain America's shield in comics a few years ago, and both characters are time-tested heroes with a close friendship in comics and film.
While it's a proud moment for the Falcon and the Marvel Cinematic Universe as a whole, this is still the missed opportunity in not having Bucky Barnes become the new Sentinel of Liberty. Both Bucky Barnes actor Sebastian Stan and Endgame directors the Anthony and Joe Russo have stated that Bucky's damaged status means that he shouldn't be trusted with a weapon. Even though Falcon is a more than worthy candidate to become the next Captain America, there are just as many reasons that Bucky could wield the shield.
Bucky, the Living Weapon
The crux of the argument against Bucky becoming Captain America makes no sense, given that Bucky uses guns and a bionic arm in the last two Avengers movies. Anyone with Bucky's level of experience and skills could be corrupted and used an instrument of evil, and Bucky was just unlucky enough to be used for misdeeds. Similarly, other heroes have been controlled by evil-doers and used in the same capacity, like when Hawkeye was controlled by Loki in the first Avengers movie.
There's also the fact that Captain America's vibranium shield is heavy. That's fine for Steve, who had some super-strength, but anyone else might struggle with the weapon in a combat situation. However, Bucky has a super-strong bionic arm, with which he could easily utilize the device.
Captain America's Legacy
In the Marvel Cinematic Universe, Steve's met Sam by complete happenstance. On the other hand, Bucky was Steve's best friend, who was there for him when Steve was just a scrawny poor kid. While they both became Steve's close friends, only Bucky was there at the beginning, and he was the only one who Steve told about his plan about to live a life with Peggy Carter, which illustrates how close the two were.
Steve's trip back in time essentially bookended the Infinity Saga. Thus, if he had chosen Bucky as the new Captain America, it could have used a character to spearhead the next chapter in the Marvel Cinematic Universe who had been present since its earliest days.
While Bucky might want to get away from his sordid past, this would be much more easily achieved in the hope inspiring visage of his best friend than in the tainted Winter Soldier title.
The Redemption of Bucky Barnes
The "damaged" status of Bucky is a poor justification for his not becoming Captain America. For one thing, Bucky was sent to Wakanda after Civil War to be rehabilitated. Thanks to Wakanda's advanced medicine and treatment techniques, Bucky's fractured psyche was probably repaired as much as his body was.
Secondly, the thematic possibilities of a man seeking redemption while operating as the new Captain America are self-evident. Regardless of t he fact that the comics already showed how this angle could work, but the MCU could use it and make it even better. Whereas that story involved Steve Rogers' death, Bucky could've been chosen by Steve himself in the MCU Accordingly, the weight of Steve's legacy would be that much heavier on Barnes, who would feel as if he was handpicked to replace a saint.
Whereas Steve became Captain America through Project: Rebirth, Bucky could've experience his own rebirth to become a better man as he learns to wield the shield. Although that would give Marvel a compelling new Captain America in Phase 4 and beyond, it doesn't seem like it will happen any time soon. In the meantime, we'll have to be content with Captain America's other partner wielding the shield.
Directed by Kari Skogland, The Falcon and The Winter Soldier stars Anthony Mackie and Sebastian Stan and will be released on Disney+. The series is expected to debut late next year.