Yelena Belova and John Walker made a huge splash with their introductions to the MCU. Yelena could certainly take up Natasha's mantle while still being her own unique and delightful self. John may not have been worthy enough to wield Cap's shield, he did turn out to be one of the most complex and engaging characters in The Falcon and the Winter Soldier.
Both Yelena and John are currently under Valentina's command, and she doesn't seem to be a by-the-book sort of leader. She could encourage their worst parts, and fans know they're not above bending the rules. They most likely won't become Avengers any time soon and leaving them as anti-heroes would give more spice to the traditionally clean-cut MCU. Only one can be the next great anti-hero, even if they both have everything it takes to go all the way.
John: His Story Was Surprisingly Compelling
Most fans expected The Falcon and the Winter Soldier to be all about Bucky and Sam, and in many ways, it was. However, the show also found the time to develop John's character, creating an impressive and occasionally moving portrayal of trauma, loss, and patriotism.
His story was unexpectedly compelling. John goes through nearly all the stages of grief during his time in the show, and he comes out stronger but more cynical. He ends TFatWS with a certain contempt for his government, even if he's still committed to being the USA's ultimate defender. This dichotomy ultimately makes him one of MCU's most intriguing characters to date.
Yelena: She Doesn't Want To Be An Avenger
Throughout Black Widow, Yelena makes constant derisive remarks about Natasha's superhero life. She makes fun of Nat's poses and speaks about her "friends" with barely concealed mockery.
Yelena isn't against being a superhero per se, but the movie does demonstrate how she finds the lifestyle bizarre and unappealing. Natasha did, too, at the beginning of her Avengers journey, yet another bridge between both characters. However, and unlike Nat, Yelena doesn't seem to want to clean the red off her ledger. She went to work for Valentina, after all, and comic book fans know the Contessa is both charming and dangerous.
John: He Got Burned By The Superhero Life
In TFatWS, John gets a taste of what it means to be a hero. He experiences the love from the crowds, the celebration that seems to follow him everywhere, and he loves it. John clearly loves to be under the spotlight, and he doesn't seem to want to keep his ego in check.
By the show's end, John's life gives a complete 180. He no longer has the support of his government or the people while also losing his best friend and even his job. John finally understands how frail and feeble a superhero's life is, something that might prepare him to go down a less honorable road.
Yelena: She's Out For Revenge
Black Widow's post-credits scene shows a still grieving Yelena visiting Natasha's grave. She receives a visit from Valentina, who encourages her to seek revenge against Clint Barton for his supposed role in Nat's death.
It's unclear how much the world knows about Black Widow's sacrifice in Avengers: Endgame, but the scene implies that the Avengers didn't explain her actions to the public. All Yelena might know is that Nat and Clint went to Vormir, and only he returned. Fans already know that Florence Pugh will show up in the upcoming Hawkeye show, but the nature or extent of her character is still a secret.
John: He Represents A New Kind Of Character In The MCU
As previously mentioned, John's character represents a contrast of ideas. He is a soldier, a man used to following orders, no matter how extreme or morally reprehensible. However, the show also makes him more cynical and less trusting of his government and its officials.
The MCU has characters like Rhodey, who believe in the system and do everything in their power to preserve it. They also have the Guardians, who purposely disrupt the system because they acknowledge its flaws. John is a new kind of character, a man who loves the system but not its participants. It will be intriguing to see how far he will be willing to go in his quest to "save" his country.
Yelena: She's Used To The Anti-Hero Life
While John loves the spotlight, Yelena does everything in her power to avoid it. She's not a "poser," on the contrary. She loves operating from the shadows and the anonymity that goes hand-in-hand with the Black Widow mantle.
Yelena always lived as an anti-hero, and she doesn't seem to want to change. Her family and all her connections also lead that anti-hero life, further reinforcing her commitment to it. Yelena also witnessed SHIELD's collapse, and as a Black Widow, knows how easy it is to overthrow regimes and institutions. She doesn't believe in any of them because she knows that humans are everything but incorruptible.
John: He Already Has Rivalry With A Hero
Even if he did sort of redeem himself at the end of TFatWS, John still has a complex relationship with the new Captain America. Sam, like Steve, places his faith in the people, not in the country or the institutions. His philosophy is to help others, no matter the cost. John isn't as selfless, nor does he place such high value on human life.
Their difference of opinions will provide some potentially deep and thought-provoking discussions should the two cross paths again, and fans hope they will. John could be the perfect foe for Sam's Cap and could feature easily feature in the upcoming Captain America 4 storylines. Like Sam, John, too, got upgraded to a job he wasn't quite prepared for and dealt with it as best as he could, confirming the contrast that inherently exists between the two.
Yelena: She's (Arguably) The Best Part Of Black Widow
There are several things in Black Widow don't exactly make sense, but pretty much everyone can agree that Yelena Belova is a highlight of the movie.
Thanks to some genuinely funny writing, a surprisingly emotional angle to her story, and Florence Pugh's charming performance, Yelena quickly cemented her place as one of the MCU's future stars. Yelena, a free agent in every sense of the word, lives by her own rules. By not being attached to a particular project, the character now has countless possibilities. Yelena is a wild card to the tee, and that makes her unbelievably alluring for audiences.
John: More Wyatt Russell
Wyatt Russell has been working for many years now. He's a recognizable actor who many fans know, but he has yet to receive a breakthrough role that will elevate him to the A-list. His performance in TFatWS was very well-received, and many believed he stood a chance at receiving an Emmy nomination.
Russell's performance added complexity and depth to John's character. He played the part, not like a villain or a hero, but as a man who received a responsibility he wasn't prepared for and ended disappointing everyone, including himself. Russell made John surprisingly vulnerable, nearly stealing the spotlight from the show's other charming foe, Baron Zemo.
Yelena: More Florence Pugh
Florence Pugh became an instant MCU star from the moment Yelena first graced the screen. Pugh irradiated charisma, injecting Yelena with such life and flare that she nearly stole the movie from Natasha.
Pugh, already an Academy Award nominee for her supporting turn in Greta Gerwig's acclaimed Little Women, is just starting with her career. She has a bright future ahead of her, and that will hopefully include a meaningful tenure in the MCU. Her arrival brightened the already incandescent universe.