In the Marvel Cinematic Universe, the superheroes are so fleshed out and three-dimensional, which makes it a shame that the villains aren't given a similar treatment. Granted, it's hard to craft a one-off villain for the hero to fight against when they are going to obviously win in the end. Still, the MCU should probably make the attempt to put as much effort into its villains as it does its heroes.
Outside of Thanos and Loki, villains in the MCU tend to be petty business partners of the heroes or average joes way out of their element. Even when a supreme dictator is thrown into the mix, they tend to be more shortsighted. Between an underdeveloped alien, a weakling weapons manufacturer, and an old man picking fights with kids, the MCU doesn't have the strongest roster of villains.
Taskmaster
On paper, Taskmaster seems strong with her preternatural ability to copy any fighting style that she sees. With this, she mimics the fighting abilities of Black Widow, Captain America, Black Panther, Spider-Man, and so many others. Despite all of the abilities at her disposal, she isn't all that powerful.
While Taskmaster might be able to mimic a vast array of fighting styles, she isn't as close to as good as the people who perfected them. Her powerful strikes and mixed martial arts skills just aren't enough to take on Black Widow, let alone the rest of the Avengers.
Iron Monger
Iron Man set a major trend for the MCU. It was the first movie to see the protagonist's business partner turn into a villain and have almost the same powers as the hero. Business between Obadiah Stane and Tony Stark turned sour, which led to Obadiah creating the Iron Monger suit.
Iron Man going up against Iron Monger wasn't exactly like going up against Thanos or even Aldrich Killian. It was more like a warm-up for Stark's more difficult battles. However, out of all the villains who are just average joes with no discernable superpowers, Iron Monger comes the closest to being a worthy adversary.
Ronan
Being a close friend of Thanos and wielding the Cosmi-Rod, Ronan looks like he should be a lot more powerful than he actually is. While he caused a lot of destruction in Guardians of the Galaxy and gave the superhero team a decent fight, what bested Ronan was one of the cringiest one-liners in the MCU.
Ronan was beaten after being distracted by Star-Lord's "dance-off, bro." On top of that, the moment he saw Captain Marvel's capabilities in the 2019 movie, he surrendered and backed away instead of trying to fight. There have been fewer weaker and embarrassing moments in the MCU than that.
Crossbones
Crossbones' role in the MCU boiled down to nothing more than a James Bond-like henchman, doing the real villain's bidding for them. Introduced in Captain America: Winter Soldier, Steve Rogers made short work of him, especially in the iconic elevator scene. During his short time in Civil War, Cap, Wanda, and Black Widow all had their turns at making mincemeat out of him.
The character might be physically strong, but that's not everything when going up against superheroes. Without the comic book-accurate suit in the opening 5 minutes of Civil War, he wouldn't have lasted as long as he did. And he didn't last that long even with the super suit.
The Vulture
Since Peter Parker is one of the most powerful characters in the MCU, it would be an injustice to say that Vulture was out of his league in dealing with the teenager. Despite being clever and sympathetic in his backstory, it doesn't mean that Vulture deserves any credit as a powerful villain.
The wings of Vulture's suit were proven to be lethal weapons in Spider-Man: Homecoming. However, in the end, they didn't cause all that much damage, and any destruction that was caused was more accidental than anything. Still, it would definitely be terrifying for anyone who dared date his daughter lest they end up under a building.
Yellowjacket
The Ant-Man movies are hugely entertaining for the way the size-changing powers of the title character and his partner Wasp are utilized. On top of that, there are so many great visual gags in the Ant-Man series too, such as Thomas the Train and the Hello Kitty Pez dispenser becoming enormous. When it comes to the series' villains, there's a lot to be desired.
The first film in the series sees Hank Pym's protege, Darren Cross, become Yellowjacket out of jealousy and daddy issues. Between threatening an old man who can't defend himself and kidnapping Cassie, an eight-year-old girl, Cross might look intimidating in his suit. In reality, he's pretty pathetic.
Ghost
Being the villain in Ant-Man and the Wasp, Ghost is yet another underwhelming antagonist in the Ant-Man series. While Ghost was weaponized by S.H.I.E.L.D., she might have an impressive superpower. Unfortunately, her abilities have far more weaknesses than strengths.
Ghost has to live in a glass box, showing her molecular disequilibrium as more of a disease than a power. On top of that, she is so easily fooled by Scott several times over. Again, while her backstory was sympathetic, it doesn't distract from her weakness as an effective villain. With the villain in the upcoming Ant-Man and the Wasp: Quantumania being Kang the Conquerer, he may put an end to Ant-Man's pattern of weak villains.
The Grandmaster
The Grandmaster is one of many villains who has other people do his dirty work for him, and without his minions, he has no power or strength whatsoever. The egotistical, power-hungry mad man isn't just weak, but he's the least powerful character in Ragnarok.
The Grandmaster isn't remotely intimidating, nor is he physically strong. While Thor: Ragnarok is great, things do slow down a lot on Sakaar, especially with Hela's plans to rule Asgard. At the end of Ragnarok the character is left on Sakaar for the people of the planet to get their revenge, he has absolutely no ability to defend himself.
Justin Hammer
More than any other villain in the MCU, Justin Hammer is just some guy. He has the same plan as Obadiah Stane in Iron Man, wanting to use Tony Stark's tech against him to create huge, almost-sentient weapons. Unlike Stane, who becomes Iron Monger, Hammer does nothing himself to combat Iron Man, and he's one of the ways Iron Man 2 aged poorly.
In Iron Man 2, Hammer hired Whiplash to try and recreate Stark's arc reactors, but that quickly backfired. In fact, Hammer made one mistake after the next. He doesn't even have control over people on his own payroll, and there's no more of a display of weakness than doing a little on-stage jig to promote his weapons. Tony Stark, he very much is not.
Zemo
Zemo is a master manipulator at times, doing a decent job of pitting Iron Man and Captain America against each other, even if the plan was riddled with plot holes. Despite helping ignite the Civil War, he has no abilities that could make him considered remotely powerful.
Zemo even knew he was no match for the Avengers, which is why he made the plan to reveal to Stark the true death of his parents. It all came down to psychological warfare for him, which every character knew about and avoided after. Now, having seen him dancing in a club in The Falcon and the Winter Soldier, it's even harder to take the villain seriously. Especially since the series somewhat redeemed him.