I mean, I don't think she was that integral to the film? At some point they could have arguably flown a ship to save Tony from space, and in the big battle at the end they might have downed Thanos' ship another way (I'd say this a stronger possibility than saving Tony, but if Marvel hadn't introduced her to the universe beforehand they could have quite easily come up with something to save Tony).

 It wasn't even about her anyway, mainly it focused on the original six. If you think a three hour long Avengers Endgame film was ruined over captain marvel I think you might be slightly obsessed.