The Marvel Cinematic Universe had developed an early reputation for its lackluster villains. Outside of Loki, no one from the first wave of MCU movies never matched up to the heroes they battled. That changed in recent years with villains like Thanos and Killmonger proving that Marvel could produce villains that at least matched up to heroes for the storyline.
The Marvel movies often build up the stories and heroes to their breaking point and then place them face-to-face with the villain, and in many cases, the final battle is underwhelming at best. With that said, when the villain matches up in power to the heroes, the battles can end up in a spectacular war where the heroes have to overcome all odds to overpower their enemy.
Overpowered - Thanos (Avengers: Endgame)
Thanos was easily the most powerful villain that has shown up in the Marvel Cinematic Universe. He single-handedly beat the Guardians of the Galaxy, destroyed Xandar, and wiped out half of the beings in the universe when he got his hands on every Infinity Stone.
He beat everyone, and it took him getting tired for Thor to stop him. However, when a past version of Thanos arrived and took on the heroes again, they finally won, but only when they overpowered him and Iron Man sacrificed his own life to conquer the Titan.
Defeated Easily - Iron Monger (Iron Man)
The idea of underwhelming villains began in the first MCU movie, Iron Man. There was a lot going on in this movie. It first showed Iron Man's origin story and the main theme was the transformation of Tony Stark into a hero.
Then, Iron Man battled a foreign terrorist cell in the start and returned to find his father's old friend performed a hostile takeover of his company. Stark finally battled Obadiah Stane, who created his own armor, and beat him easily in their final battle.
Overpowered - Killmonger (Black Panther)
One of the most critically acclaimed MCU movies was Black Panther, with viewers discovering the wonderful world of Wakanda. However, once T'Challa became the King, he faced two different obstacles. The first was a rival chief in M'Baku, but T'Challa beat him.
The next was Killmonger. Not only did Killmonger beat Black Panther handily in their first battle, but he took Panther to the limit in their final battle, which was when Panther forced to kill his rival to win.
Defeated Easily - Surtur (Thor: Ragnarok)
Thor: Ragnarok was the first Thor movie that saw fans and critics both praise it, and it gave a new life to the God of Thunder, who will become the first MCU hero to get a fourth solo movie. In Ragnarok, Thor started the movie held captive by Surtur, the demon fated to bring about Ragnarok, the end of Asgard.
Thor quickly freed himself, attacked Surtur, and without much of a fight, he destroyed Surtur and took his crown. Thor then escaped Surtur's realm and returned to Asgard with his trophy.
Overpowered - Hela (Thor: Ragnarok)
While Thor beat Surtur easily at the start of Thor: Ragnarok, he had a much harder battle when his sister Hela arrived. Odin died, and when he was gone, it freed Hela from the prison he had placed her in.
Hela came back to take over Asgard and killed every member of the Asgardian army, including the Warriors Three. Thor and Loki combined couldn't beat her and it took releasing Surtur and destroying Asgard to finally overpower the Goddess of Death.
Defeated Easily - Yellowjacket (Ant-Man)
The first Ant-Man movie was basically a heist story. Scott Lang received his release from prison and wanted to do good, but he couldn't keep a job due to his prison record. He got a chance for "one last heist," and it involved breaking into Hank Pym's home and stealing the Ant-Man costume.
Lang ended up helping Pym when an unscrupulous business partner, Darren Cross, tried to sell Pym Particles to the highest bidder. It resulted in a final fight between Ant-Man and Cross, who took on the role of Yellowjacket, and Cross never really stood a chance.
Overpowered - Ultron (Avengers: Age of Ultron)
The Avengers originally formed because Earth needed its most powerful heroes to battle powerful forces of evil. This included an alien invasion in the first Avengers movie and Thanos in the third and fourth. The second movie, Avengers: Age of Ultron, also included an almost unbeatable villain.
Tony Stark created Ultron to be a force to help battle and save the planet. However, when Ultron realized humans were the greatest threat to the planet, the robot set out to destroy them and it took their combined forces to finally overpower him and stop his reign of terror.
Defeated Easily - Loki (The Avengers)
The first Avengers movie saw the team in a massive battle to save Earth from an alien invasion. Loki partnered with Thanos to send the Chitauri to attack the planet. The Avengers barely beat the aliens and finally got rid of them when Iron Man closed the wormhole.
However, once the aliens were gone, they battled Loki in the end and they had no problem bringing down the God of Mischief, with Hulk just destroying him.
Overpowered - Ego (Guardians of the Galaxy Vol. 2)
Ego is a celestial, so there is no way he goes down without a major fight. In Guardians of the Galaxy Vol. 2, the team had two big reasons that they struggled to beat him. The first was that he was Peter Quill's dad, and he was able to separate his son from the group.
Second, he is a celestial who has powers that dwarves every member of the Guardians combined. They only beat him because Mantis knew about the core of his body and they really didn't destroy him — they just stopped him and escaped.
Defeated Easily - Yon-Rogg (Captain Marvel)
Captain Marvel set Carol Danvers against who she thought was the enemy with the Skrulls on Earth. However, when Carol learned that the Skrulls were hiding from the evil Kree, and Captain Marvel worked for the Kree, that put her in a tough spot.
Captain Marvel took the side of good and fought against her former Kree allies. It all came down to Carol vs. Yon-Rogg, the Kree warrior who trained her. However, by this time, Captain Marvel gained more powers and Yon-Rogg never stood a chance in their final battle, falling easily.