If you're a comic fan, the Marvel Cinematic Universe isn't made for you.
It's no secret that the Marvel Cinematic Universe is the single most important and influential cinematic endevour ever to be produced. Spanning 22 cinema released feature films, and 12 spin-off TV shows. While more is being produced, the overarching story that has culminated with the film 'Avengers: Endgame' is contained within these; with the potential for it to spin outwards in almost any direction. Adding to the MCU with more and more, including prequels and addition spin-offs will allow for those numbers to continuously increase. In fact of the 12 shows only one of them directly crosses over with the films significantly, that being 'Agents Of SHIELD', and none of the shows directly alter the films plotlines; so it could be argued that the TV shows represent an expanded universe rather than the main continuity. Either way the MCU is the single biggest franchise universe ever made, with the films alone taking over 47 hours to watch.
It's honestly amazing to consider just how huge this is. 'Avengers: Endgame' isn't just a 3 hour epic where the heroes from the previous films come together in a final chapter tying everything else together. It is that, but it's also an indication of shared culture. Even if you've not seen everything the MCU has to offer, even if you've watched only some of the films. As a bare minimum to understand the last film in this series you need to have seen the three previous 'Avengers' films, the first 'Guardians Of The Galaxy', 'Thor: Ragnarok', and 'Captain America: Civil War'. (It would also helpt to have seen 'Thor: Dark World' as it directly ties in to 'Endgame' but then so do a lot of the films). Just having seen those 6 films prior to 'Endgame' would represent 17 hours of investment into the MCU and while this is anecdotal, most people I've spoken to have watched far more than just the bare minimum. That's a level of time investment previously unheard of in any film franchise.
I highlight this because I want to make it crystal clear how unlikely it is that people would take the time to watch and understand the MCU. Most people work or study, have families and other responsibilities, or simply have other hobbies occupying their time. Most people don't have the time or inclination to sit through literal days of self-indulgent cinema, and that's what the MCU is really; and yet they do by the millions. Literally millions of people watch these films and at the time of writing 'Avengers: Endgame' is the world record holder for largest box office opening of all time. This is the biggest film ever made, and it's based on a comic book... and yet it is categorically NOT made for comic book fans.
Don't get me wrong. This isn't some identity politics rant about how these films aren't for "straight white men", because I'm not a simpering bigoted cunt like Brie Larson, who thinks your skin colour, ethnicity, or sexual orientation makes any difference to the cinema you enjoy; nor do I feel you solve the issue of historic oppression by oppressing those who share an identifing label they have no control over, with the oppressors in question but who individually had fuck all to do with any of it. So, no as a white man I don't feel guilty for the African slave trade, nor do I feel ashamed for the lack of women's rights before the Sufferage movement. Why? Because I wasn't fucking there! I didn't take part in any of it, I didn't endorse any of it, and frankly the ethnic minorities and women who complain about this shit, also weren't the goddamn victims of it. You don't get to claim victimhood for something that happened to someone else because your skin-tone happens to match you self-absorbed self-obsessed arrogant bigoted arseholes.
So no; this isn't some gatekeeping attempt, nor is this bigotry in the name of "equality" in an attempt to virtue signal to the SJW movements. No, this is a statement of fact. If you are a fan of comic books the Marvel Cinematic Universe is categorically not made for you. So while I regularly hear people complaining that the films "didn't follow the source material", those complaints are being ignored because literally no-one cares... statistically speaking.
You see the average comic sells approximately 30,000 to 75,000 copies during it's print run, with extremely popular releases maybe topping the 100,000 sales number. The MCU films on the other hand usually top $500 million at the box office; with the biggest films breaking the $1 BILLION figure. At $15 per ticket (which is a gross overestimation of cost), and assuming half the people who see the film will go back and see it a second time (which is again a massive overestimation), that would mean a film that makes $500 million at the box office is playing to around 8-9 million viewers; and that an extremely lowball estimate. Let's round that up to 10 million for ease of use.
If 10 million people watch these films on average, (that's 10,000,000 just for context), and let's overestimate and say 100,000 are buying the comics; that means in a standard cinema screen which can hold around 400 seats; only 4 people in the room will have actually read the comic. That is the reality of the situation. Less than 1% of the cinema going public read comics, and if we run the figures with films like 'Captain Marvel' where the comic struggles to sell 30,000 copies and yet the film managed more than $900 million at the box office; only 0.15% of the people who saw that in the cinema have read the comic. That's less than one person per screening, or only 3 people out of every 2,000 people who saw the film.
In short when people complain about films following the source material they're just being contrarian. They're trying to gatekeep. They're saying, "I'm a real fan, and you're not because you've ONLY seen the films". It doesn't matter if it's a comic adaptation, a book adaptation, or even an anime adaptation; there are always those arseholes who think they get to dictate who can enjoy this new interpretation based on a previous media's take on the subject. The fact is, cinema is the predominent form of entertainment in our culture, (though video games are challenging it in financial output, in sheer numbers cinema is still an order of magnitude more impactful in it's reach). People need to accept that adaptive works in other mediums aren't trying to be perfect re-creations, they're trying to be their own thing. They're trying to express the key ideas, the themes of the original work and make it fit the new challenges of the medium.
I am a pretty geeky guy by all accounts. I'm a gamer, a sci-fi fan, and a film buff. I've collected Warhammer models, Magic: The Gathering cards, and play tabletop RPGs like Shadowrun and Dungeons & Dragons; (and have done for decades). I've been playing video games for almost 3 decades, and I've a DVD and blu-ray collection of more than 600 films and TV shows. I am the archetypical geek and I would consider myself a fan of the MCU. I've seen every film, and most of the TV shows (though I've not got around to watching some of them). I have NEVER read an Avengers comic. Even people as entrenched in geek culture as I am don't always read the comics.
Ultimately we have to accept that not everything is made for "the fans", depending on how you define such a group. Not everything will be the same. Poetic licence and creative liberty has to be given when things change medium. That's the take away here. There's no need to be a fanboy or fangirl. If you prefer the way it was done in the comic, great, you can still read the comic if you want; but don't expect perfect re-creations. It's expectations like this that only serve to ruin the final product for you; and wouldn't that be a waste for the 1% of you out there who already care about these properties?