While the Marvel Cinematic Universe is full of characters that are nuanced and exceptionally layered, there are also a few that just completely missed the mark. These characters are disappointing not because of what they do to other characters but because they have quite simply been ruined or underutilized by Marvel.
Reddit users have readily given their input on which characters disappoint them the most, most of which are unanimously agreed on. Even though these characters make the list there is still hope that these will be restructured and reintroduced, however, till that happens these disappointments reign strong in the fandom.
"Fietro"/Ralph Bohner
Everyone was extremely excited when rumors started floating about that a variant of Pietro - Fake Pietro a.k.a. Fietro - would be showing up in WandaVision. Unfortunately, when he actually did show up it was extremely underwhelming and more than anything else, disheartening to see a character so interesting being used as a throwaway. Not only that, he was made into a punch line that just didn’t land.
After seeing Evan Peters portray Quicksilver in X-Men fans had high hopes that were thrown off the top of a skyscraper with no care about their feelings. The disappointment with this character can still be largely excused as the entire intention behind it was to be "the best troll ever," as pointed out by Samantha_Cruz.
Ronan
Ronan first showed up in Guardians Of The Galaxy as the main villain and henchman of Thanos. Though a considerable improvement from the other characters on this list, he still brings a tinge of disappointment to Marvel fans because of his underutilization and unidimensionality.
silverBruise_32 makes a great point on how his character was ruined by saying, "A complex character, turned into a religious fanatic and killed off in his first movie." His character is once again underutilized when he shows up in Captain Marvel for the briefest of moments as a hologram.
Sharon Carter
After debuting in Captain America: The Winter Soldier there was a lot of potential for Sharon Carter‘s character. Unfortunately, by the end of Captain America: Civil War she had, very simply, been diluted down to Steve Rogers‘s girlfriend - creating an uncomfortable situation for fans as she's Peggy Carter’s niece.
As TailorChemical mentions, "I personally think they've wasted Emily (the actress) so far and the character hasn't been interesting outside a few moments." With The Falcon and The Winer Soldier setting up Sharon's future, hopefully fans will get to see more of her - though Sharon turning evil after being brought up surrounded by the "good guys" seems to go against her character.
Kro
While Eternals as a whole was received with extremely mixed reviews, a lot of viewers can unanimously agree on the fact that Kro's character - the leader of the Deviants - just wasn’t good enough. Frustratingly, his character was of no use to the plot or to the other characters.
Redditor RaynSideways accurately states, "All this buildup for how different and important he is and he just sort of shows up at the final battle without a specific reason to be there other than that's where all the Eternals are." Additionally, due to his premature death, viewers are unsure if they'll get any redemption for his character's treatment.
Drax
Dave Batista isn’t the only one who dislikes Drax's character development. A lot of fans have commented on how his character went from someone who should have been a force to be reckoned with to, very simply, someone used mostly as comic relief.
Turbulent-Gazelle629 makes a similar case saying, "when I first heard when he came into the MCU I was so hyped because I know him from the comics. I personally think there's a lot of wasted potential when it comes to Drax," and they aren't wrong. His backstory is so deeply rich that it can create a multi-dimensional character, one that viewers got a glimpse of during his chat with Mantis on Ego's Planet and hope to get again in Guardians Of The Galaxy Vol. III.
Crossbones
Marvel fans have long since noted that Captain America's villains have a tendency to have the same treatment, one where they all get killed off before coming into their own and becoming the threats they are in the comics. The same happens with Crossbones a.k.a. Brock Rumlow who dies in Civil War.
The most annoying part of his character's treatment is that, after spending the entirety of The Winter Soldier as Rumlow, he is killed off minutes after he's introduced as Crossbones in the third movie. Instead of that, they could have saved his character and. as DukeCaleb points out, "I would have much preferred him to come back and be a villain for Sam's Captain America."
Hulk
Fans have become increasingly frustrated with where Hulk's storyline has brought him. In Thor: Ragnarok, viewers got to see a version of Hulk that impressed them, a perfect split between him and his alter-ego. Unfortunately, ever since his showdown with Thanos he continuously became more and more like Bruce Banner, departing from the Hulk seen since The Avengers.
People within the MCU also seem to have forgotten that he was also an essential part of bringing everyone back. A lot of fans also dislike that he never got his redemption arc with Thanos with pianoceo saying "You have this incredible character who didn’t get a chance at revenge, who has an unlimited amount of power, in a fight for humanities escape from the edge of annihilation. It’s just super disappointing to me."
Malekith
Thor: The Dark World has been called one of the most disappointing movies by many Marvel fans and this characterization probably boils down to one reason - an extremely one-dimensional villain. The Malekith seen on the big screen is drastically different from the savage and downright unhinged with a lot of Reddit users comparing his behavior to the likes of the Joker. To make matters worse, it's a gross underutilization of an actor like Christopher Eccleston.
As xnarphigle points out, "Malekith is a complete opposite as to what he is in the comics." Another user, Whitluck, provides further insight saying, "He was supposed to be a moral reflection for Thor to compare himself to... It was never fully realized and we missed out on a potentially fantastic villain."
Pietro Maximoff
Pietro Maximoff is on the list of the most disappointing characters twice for Reddit, this time for Avengers: Age of Ultron. A lot of fans thought that Marvel missed out on the opportunity to capitalize on a new character played by an exceptional actor. Moreover, his death was not only extremely premature but was also used for the sake of a plot twist rather than an actual plot development point - other than putting Wanda through pain.
The possibilities for Pietro, especially after Infinity War and Endgame, and subsequent implications of Wanda's storyline were endless. As PreTry94 lays it out, "the timeline where Pietro lives sounds infinitely more interesting than any twist they could've pulled in AoU. Imagine... he continues to help in Infinity War, but is not dusted, separating him from his sister... then when Hulk brings them all back, he is 5 years older than his twin sister."
Taskmaster
Reddit users very unanimously agree that Taskmaster from Black Widow has been the most disappointing character to date in the MCU. This disappointment doesn't stem from the fact that the character's gender was changed. Instead, it's because the character itself was decimated from what they're portrayed as in the comics.
There are a lot of angry Redditors, KeineSchneit in this particular instance, that hate what was done to the character stating, "the portrayal of Taskmaster physically upset me. Such an amazing and important character reduced to that horse****." Similar to what Marvel did with the Mandarin, there may still be hope for redemption of Taskmaster's character portrayal, as well as many of the other characters on this list, and that’s something that fans are holding onto with bated breath