Marvel has a villain problem. Anyone who is a fan of superhero comics or superhero media in general will tell you that the villains are often the best part of any superhero story. Villains keep things interesting and challenge the hero, and if they're done right, they're usually just a lot of fun to watch. Marvel has done well with villains in the past, but lately it seems that they've fallen into a rut where the villains all feel very similar and don't do a lot to distinguish themselves, which leads to them becoming the more forgettable parts of their respective movies.
Villain redemption arcs are usually interesting, but it seems like the MCU has really been relying heavily on that kind of storyline. Many of the recent villains have been people who were doing bad things but then changed their minds when the hero talks some sense into them, or characters who were never really villains in the first place, just a good person who momentarily fell down the wrong path. These could theoretically be interesting in their own ways, but having too many in a row makes the stories feel predictable. Marvel needs to start including some villains that are purely evil for the sake of being evil and don't get redemption by the end of their stories in order to shake things up in the MCU again.
Marvel's Favorite Kinds of Villains
It's been a long time since Marvel has had a villain that was just a one-off and died at the end of the movie without any sort of redemption storyline. Of course, if every villain was like this it would be just as boring as if every villain got a redemption arc, so there needs to be a solid mix. The more recent MCU movies have had a couple different favorite kinds of villains, the first of which are those that are heavily connected to the hero in some way, such as a family member, who gets some sort of redemption or ends up sacrificing themselves heroically (like Wenwu in Shang-Chi and the Legend of the Ten Rings or Ikarus in Eternals). This is an easy way to raise the stakes for the heroes and get them immediately invested in the action, and it often leads to a lot of emotional conflict.
The other type of villain that's been appearing in a lot of Marvel stories recently is the "antagonist who has a good point but is going about it the wrong way". This is when the villain of the story is shown to have a goal or moral quest that is noble in its own way, but they use violence or manipulation to achieve that end goal (such as Killmonger in Black Panther or Karli Morgenthau in The Falcon and The Winter Soldier). This began as a way to challenge the heroes and make them rethink the ways in which they carry out justice, and when used correctly (and sparingly) can be really interesting, but when it's overused, it seems like the creators are almost trying to shut down more progressive ways of viewing the world because the characters are going "too far".
Again, on their own, these types of villains are engaging and make the stories that they're in more interesting. But when every recent Marvel antagonist can fall into one of these categories, they all start to blend together and become increasingly predictable. Willem Defoe's return as the Green Goblin in Spider-Man: No Way Home felt really refreshing (despite it being a rehash of an old character) because it was fun to see a villain who was just sadistic and evil. Of course, the Green Goblin is a special case because Norman Osborn is still a sympathetic character who's not in control of his actions, and the entire point of No Way Home is that Peter is trying to redeem these villains, so even that didn't really bring back a classic evil villain formula.
Making Villains Evil Again
A great example of a villain who's just evil and never redeemed is Ultron in Avengers: Age of Ultron. He was just a straight-up bad guy that the heroes had to defeat, without worrying about "saving" him. This also allowed him to be fun, and many fans praise James Spader's performance as being one of the best parts of the movie. Other villains like Hela, Red Skull, or Obadiah Stane can fall into this category as well, though many of them aren't exactly over-the-top fun, and many still have some sort of familial connection to the heroes (like Hela or Ego, who are embodiments of evil and have big personalities, but are still connected to the protagonists).
Phase 4 is devoid of any villains that resemble this, as most of them fall into the previously mentioned categories. Dreykov from Black Widow may be the one exception, but he still has ties back to Natasha's past. Again, this kind of villain can be interesting in its own way, and it's great that Marvel apparently wants to tell more nuanced stories with complex characters, but lately they've been missing out on the pure fun that a really evil baddie can bring to a superhero movie. Comic book villains are fun because they're often over-the-top or bombastic, but the MCU has tried to ground itself so much that the villains don't really pop as much, especially in this newest phase.
Loki introduced the idea of Kang the Conqueror into the fold, and it's possible that they could be setting him up to be a big, unsympathetic bad guy that will pop up throughout Phase 4 (or at the very least, be the next big bad after Thanos). This could be really interesting and provide them with an opportunity to rediscover what makes villains fun and try to integrate some of that back into the movies and TV shows. If the MCU wants to keep things fresh in Phase 4, it would be wise of them to fix their villain problem and make it so that every villain doesn't feel like a slight variation on the same character. Villains are meant to be fun and menacing, and it's been too long since the MCU has had one that truly embodies those qualities.