Are you kidding me ? Spider-Man is not a big shot in the Marvel universe ? He's like, the most known superhero Marvel have. If anything, he's right after Batman and Superman in terms of being "big shot". Now please don't go all hipster on me telling me how Black Panther or Ms Marvel is bigger than him.
Are you talking about in real life or the Marvel universe? I'm talking about the Marvel universe. Yes, he is the most known superhero Marvel has but that is in our world. If we all lived in the Marvel universe right now, that wouldn't be the case. People like Iron Man, Cap, Thor, and the Fantastic Four are all more well known and are generally more liked than Spider-Man in the Marvel universe (once again, the Marvel universe; not the real world). On the other hand, this doesn't apply to Batman and Superman. They're the top big shots and most well known superheroes in both the DC universe and here in the real world.
Black Panther and Ms. Marvel aren't bigger but they deserve to be in an Avengers sequel more than Spider-Man. Spidey is great as a one man show, Ms. Marvel and Panther are perfect for Avengers especially Ms. Marvel who probably will never have a solo movie. Not to mention they both are better known as Avengers than Spidey.
Agreed. I'm not against the idea of Spider-Man coming in but the importance of characters like Ms. Marvel, Black Panther, Vision, Ant-Man, and Wasp come first because they're iconic Avengers characters. However, if Marvel has already made the decision to bring in Spider-Man at one point if they can, I believe what I said before would apply.