Numerous Loki scenes from 2011's Tom Hiddleston's God of Mischief is clearly a villain in Thor. From the start of the movie, Loki is plotting against Chris Hemsworth's God of Thunder, giving him the idea to go to Jotunheim against Odin's (Anthony Hopkins) wishes and trying to take the throne of Asgard for himself. The reveal that Loki is a Frost Giant and his parents kept his true lineage from him makes the character's journey more sympathetic, but his mischievous ways are always present.
Thor sets up Loki as a worthy villain for 2012's change Loki goes through in Avengers. In that film, Loki's need for power turns him into a cold monster. On Earth, he leads an attack by the Chitauri aliens, kills dozens of people, and shows little to no remorse. He's a worthy Avengers adversary.
Some key deleted scenes from Thor allowed Loki to make his transformation into full-on villainy. Though Loki's tragic backstory makes him somewhat sympathetic in Thor, it turns out the character could've been even more endearing to audiences. Various deleted scenes from Thor (via Loki's mother, Frigga (Rene Russo) talking to him about the decision to keep his parentage from him. He's even surprised when she offers him the Asgardian throne while Odin is incapacitated in Odinsleep. The scenes don't change the fact that Loki is the villain of the story, but they aggressively humanize the character.
Had the scenes made the final cut of Thor, they could've confused audiences watching The Avengers. The 2012 movie was Marvel's first attempt at bringing its heroes all together. Ahead of the MCU, sprawling shared universe movies weren't really a thing, and Avengers was the proof of concept. The movie relied on fans getting behind its heroes in a classic good vs. evil battle, and Loki's deleted scenes could've destroyed it. If the various Loki moments were left in Thor, it'd make Loki's jump to the villain of the film bizarre. Why was Loki suddenly a power-hungry sociopath when Thor presented him as a loving brother and a caring son?
If The Avengers didn't work, the MCU wouldn't exist as it does today. As it stands, Marvel has released more than twenty films and is now expanding on its shared universe with critically-praised TV. With its success, the MCU is also breaking new ground in comic book films, bringing a new Asian superhero in Shang-Chi and the Legend of the Ten Rings and confirming that the God of Mischief is bisexual in Loki. Yes, the Loki scenes would've made the character more heartbreaking in Thor. But by leaving the scenes in, Marvel may have ultimately killed more Marvel superheroes than Thanos.
