Marvel may have forgotten how powerful Spider-Man truly is, but they haven't forgotten that he was a part of the Avengers. Spider-Man is one of the most recognizable superheroes of all time, so it's no surprise that he would be part of one of the most recognizable superhero teams.
In order to be part of Earth's Mightiest Heroes, a person has to exhibit numerous traits, including heroism, bravery, and sacrifice. Through his various MCU quotes, Spider-Man has revealed more than just these attributes, thus proving why he is the best Avenger.
"You Have A Metal Arm? That Is Awesome, Dude!"
Spider-Man To Bucky In Captain America: Civil War
Fans were ecstatic when Spider-Man made his MCU debut via Captain America: Civil War, and for good reason. There was finally a comic book accurate portrayal of the web-slinger.
Among one of Spider-Man's most notable traits is his humor. It reflects his age, as shown in the quote above. He is so captivated by the moment that he can't help being starstruck (Falcon even points this out). Spidey's humor makes him a perfect Avenger in that he brings levity to the team. While Thor has become comic relief, Spider-Man did it first without being a parody of himself.
"Everyone She Helped; They'll Keep It Going."
Peter Parker To Happy In Spider-Man: No Way Home
No Way Home was an important step in Peter Parker's character as Aunt May and her resulting death was a big influence on him.
Peter realized he had to accept that she was never coming back. However, he can keep her memory alive by being as selfless as she was. He shows this by sacrificing his happiness with MJ and friendship with Ned. Peter was willing to move on and change with the world. He learned from past mistakes, resulting in his progression, not only as a person but a hero as well. Spider-Man's selflessness is a true sign of an Avenger.
"I'm Sick Of Mr. Stark Treating Me Like A Kid."
Peter Parker To Ned Leeds In Spider-Man: Homecoming
Spider-Man is definitely the youngest member of the Avengers. He doesn't like to be reminded of it, as Tony Stark always seems to do. Peter, deep down, knows that he is the youngest and that he has to prove himself to his fellow superheroes.
There are positives and negatives to Peter thinking this way. He was in over his head, trying to capture Adrian Toomes' associates on the Staten Island Ferry, and even more so when trying to take down the Vulture himself. Despite these missteps, Spider-Man's bravery can't be understated. The fact that he's only a high schooler willing to risk his life and show bravery in the face of great adversity is often overlooked.
"I'm Not Iron Man."
Peter Parker To Happy In Spider-Man: Far From Home
One of the more emotional moments Spider-Man faces is in Far From Home. Peter knows that he could be the cause of thousands of deaths by inadvertently aiding Quinton Beck.
One of the cringiest parts in the MCU Spider-Man films is Peter's over-reliance on Tony Stark (it was even assumed Spider-Man would take up Tony's mantle after Tony's sacrifice in Endgame). Peter's moment of disappointment showed that he has to be Spider-Man and not Iron Man. This breaking point of realization made Peter stronger and more focused, as he knew he was the only one that could take down Mysterio.
"So, To Become An Avenger, Are There Like Trials Or An Interview?"
Peter Parker To Tony Stark In Spider-Man: Homecoming
From the moment Peter met Tony, he dreamed of becoming an Avenger. He officially became one in Infinity War. It's his eagerness and excitement that sets Spider-Man apart from the other Avengers.
The original Avengers team was assembled via the Avengers Initiative by Nick Fury. None of the members had the ambition that Spider-Man has in joining the team, as they were already chosen. In fact, many of them were reluctant at the idea, because, as Bruce Banner put it, they were a "time bomb." It's far more rewarding to earn a roster spot on the team as Spider-Man does rather than already be on it.
"I Don't Want To Brag, But I Will. I Was In The Avengers."
Peter Parker 1 To Peter 2 and Peter 3 In Spider-Man: No Way Home
No Way Home was a crowd pleaser when all three Spider-Men teamed up to fight their universes' respective villains. However, there's more to this than just an eruption of applause.
Tom Holland's Peter Parker is the youngest of the three, much like he is when being compared to the rest of the Avengers. Unlike with the Avengers, he takes charge of the group. Peter takes everything he has been taught throughout the previous films and used it to lead the trio, ultimately being able to save the villains from their inevitable fate. Because of the confidence Peter gained by being an Avenger, the inclination to take charge seemed almost natural.
"... They Happen Because Of You."
Peter Parker To Tony Stark In Captain America: Civil War
"When you can do the things I can, but you don't, and then the bad things happen...they happen because of you."
This above is a variation of the "With great power comes great responsibility" quote said by Uncle Ben. Although Uncle Ben is never acknowledged in the MCU films yet, Aunt May makes up for it with one of the saddest quotes from Phase Four.
It's probably one of the most important lessons that's bestowed upon Peter - responsibility. It's also a key attribute of being an Avenger and Spider-Man captures it perfectly. When Tony asks Peter why Peter does what he does, Peter responds with the above quote. Tony knew instantly that Peter had the potential to become a worthy Avenger, as Peter acknowledged his own power, yet was able to have the responsibility to keep it in check.
"Come on, Peter. Come on, Spider-Man."
Peter Parker To Himself In Spider-Man: Homecoming
Out of all the adversity that Spider-Man has experienced, one moment in particular stands out from Homecoming. After his failed attempt to stop the Vulture, Peter finds himself under rubble, unable to escape. He starts screaming for help, but to no avail.
Upon remembering Tony's words about Peter having to "earn the suit," Peter had an epiphany. He had to dig deep within himself in order to get free. Just thinking he was Spider-Man wasn't enough - he had to say it out loud and truly believe it. This belief in himself gave him the strength to lift the rubble.
"Thank You, Mr. Stark, But I'm Good."
Peter Parker To Tony Stark In Spider-Man: Homecoming
At the end of Homecoming, Peter finally got his chance to become an Avenger, complete with a brand-new suit. However, he did something that not even Tony expected.
A new suit meant becoming an Avenger, and this was a major event in Spider-Man's life. Tony offered the suit because Peter showed responsibility, but Peter showed maturity by turning it down. Even though he came into his own as a hero (and then some), Peter felt he wasn't quite ready and wanted to keep his feet on the ground for a little while longer. Tony was pleasantly surprised at Peter's maturity, even returning his old suit to him.
"You Can't Be A Friendly Neighborhood Spider-Man If There's No Neighborhood."
Peter Parker To Tony Stark In Avengers: Infinity War
Peter did attain the upgraded suit in Infinity War, yet that didn't change his viewpoint on how he approached helping people. Tony is angry at Spider-Man for stowing away on one of Thanos' Q-Ships in order to rescue Dr. Strange from Ebony Maw. However, Peter defends himself with this quote.
Although it seems corny, it speaks volumes about him. Spider-Man wants to fight for the "little guy" as he has stated numerous times before. In order to do that, risks have to be taken. This is the fundamental aspect of being an Avenger - the ability and willingness to defend those who can't defend themselves.