I really wouldn't over think it. These are all fairly daft films, predictably telegraphed by 50 years of source material and never really intended for a serious cross examination.
@Sylar has probably said all that needs to be said, I'd only add; wait and see what happens in a couple of weeks. Whatever the outcome, it won't be worse than Ultron, The Dark World or Iron Man 3.
Thinking about these things make them more enjoyable than just taking it in, bad or not, and moving on. Even if they are superhero films, it doesn't mean they can't be cohesive and well written or take you on a journey that leaves an impression, which is why, as you've done yourself, we can tier these films and say what's dire, average or good.
I don't really get why people feel talking these films down has any merit when they, like everyone else, invests time and money in watching them.
I've stated multiple times in the past, that some of these films are definitely cinematic experiences that don't stand up without the spectacle, or certainly won't leave the same impression on you if you look at them objectively without the razzmatazz and over stimulation you can get at the cinema, but I would always hope to see films where the writers and directors have tried to provide both the former and the latter. I also think, on the whole, these MCU films are improving so you do hope that trend continues across franchises.
See, the problem is they had a few ways to introduce her but each one would have seen issues:
1) If they had introduced her previously, then the question throughout the whole of IW is where is she? Now its at most, why wasnt she called (after the fact).
2) If they intro her during Endgame, imo its actually worse (esp as her powers would have been established in that movie rather than before) - I think the anticipation of her and Thor going at it with Thanos is great.
3) if they dont introduce her at all, then basically its left to the same avengers from the first movie (but basically half of them).
I think the one point is what
@beedoubleyou stated, it doesnt need much over thinking. Its not trying to be something it isnt, its meant to be a fun adaptation brought to screen of heroes kicking villains asses. Captain marvel is a kickass hero.
Her own movie did what it needed to, intro'd her, established her history, her powers and that she has control over it. And is ready to come back to Earth to join up with the rest due to the emergency state.
I think it will be a fun climax and her addition is a welcome one.
To
1. That's easy - she's on the 'other side of the universe/galaxy' and preoccupied with some other villain with comms to her either not working or being interfered with by some other big, old meany. Hell, they could even have her going through her own tribulations as an inferior fighting for her own life etc.
2. Ties in with 1. you definitely don't want her introduced too late, unless Thanos 'Hulks' her, and we're instead dosed with more girlpower, it's going to be extremely anti-climatic a finale to literal decades of hard work and construct.
Your bolded really is glossing over all the gripes I and others in here have stated in saying the film barely does any of that and makes her seem detached and, effectively a trump card pulled out of nowhere (her film coming far too late) they missed a huge opportunity to insert the character, who is clearly integral, in a more seamless and agreeable way.
I feel exposition for extremely powerful characters is multiples more important than it is for lesser ones and by comparison, they were painstaking in slowly upping Thor's power before having him max out, finally, in his third film (onward), and look at what they've done with Hulk!
As I said in my earlier post, Superman has the same issues and it's why they're in a corner with him until the Darkseid's and Doomsday's enter the fray, even then, Superman is a multi-layered character compared to what they've offered up with Captain Marvel in this film.
I'm not going to call it a bad film, but at the same time, they've missed a trick, or several, with the way it has been written and that won't be rectified in End Game unless she's put through the mill and isn't just an easy saves the day character.