Second, and I understand you have no problem with this, but it's kind of deflating to think that we've been building up some grand narrative about the fate of the universe and the biggest battle against the greatest villain only to introduce a character two months before the ending and saying she's been doing stuff like this for 30 years.
It really, really, really isn't to me. I cannot begin to tell you how much it isn't. If I could have all 6 infinity stones and used them to write a post with the most immaculate wording and language man could use, I still probably would not be able to tell you how much I do not believe this affects mine or most people's interpretations of a work.
I'm not even convinced I should concede to this as a difference of opinions either, because we have proof of it not being an issue in other instances. Tell me, what possible comparison in terms of stakes is there in Peter Parker stopping the Vulture from stealing Stark's weapons at the end of Homecoming if you know for a fact there are transdimentional threats to the existence of reality itself as established by Dormammu in Doctor Strange? The former could probably cleaned up by Iron Man afterwards if Peter fails to stop him, but no one, not even Captain Marvel, could concievably help Strange against fucking Dormammu. It's possible Dormammu is a higher being than even Thanos since whatever plane of existance he is on, it doesn't seem to operate by normal rules.
And yet people still cared about Peter saving the day. In fact, I would argue that people cared more about spiderman stopping this low-level glorfied thug baddy than they cared about Strange stopping a lovecraftian terror, if reception is anything to go by. And it's not even just because it was saving the day, but because that fight was Peter self actualizing into the hero that he is meant to be. That's how narratives work, they make you care about the person whose story they are about. It doesn't matter that Strange has biggers stakes in comparison because if we care about peter, and he cares about stopping vulture, then we're invested in that outcome, no matter how small scale it is to anyone else.
What your describing is not how stories work. That's not how they ever worked. If you honestly feel that the story was diminished for you because Captain Marvel has other high stakes shit to take care of, well, I can't speak to your personal feelings obviously, but I don't think you should say it applies to other people in general, because I feel it
provably does not. I feel your just incorrect on this one, atleast outside yourself. If nothing else, doesn't the fact that you are the only one who has brought up this point as an issue speak to that at all?
It's a bit like if at some point in GoT some character landed in the Iron Island and said "Oh, you're dealing with the ice zombies threat? I can help you, I've already dealth with the sand zombies, and the stone zombies, and the pannacotta zombies, and the silk zombies. There's been zombie emergencies like these all over the world! You guys will be fine".
That analogy doesn't really work because to equate it to how it happened in Avengers, you'd have to have this character not available until the last moment where the ice zombie apocalypse already started. Like, remember, even though Carol is provably stronger than Thanos, she arrived so late and got outfought due to Thanos's quick thinking. If Tony hadn't made his move, Thanos would have won.
So this would be more like if the ice zombies already invaded, killed several characters you care about, and for all their knowledge this character still would not be able to defeat them on their own.