MCU is a different story because from the get go they never intended to adapt the comics plus most people who actually watch the films couldn't really give a shit in the first place what the comics did.

It's not necessarily the same within the anime and manga community because our communities are much more connected. Even if you are an anime only watcher you are going to know if they change something usually because someone else will bring it up.

Ultimately no not every adaptation needs to be a 1 to 1 remake and some can benefit in sometimes changing what a manga has done due to the nature of the medium, story reasons etc. Problem is it feels changes often occur because they need to save time and that isn't going to be popular for obvious reasons.