"You gotta keep in mind what’s interesting to you as an audience, not what’s fun to do as a writer." - Emma Coats, Pixar.
I recently read some articles, in the aftermath of Avengers: Endgame, that suggested that the writers wanted to include an encounter between the main villain, Thanos, and a cosmic super-entity called The Living Tribunal.
Avid comic book readers would surely know this character better than I would. I can't say for certain whether this is an interesting character or not, or whether this would be a fun encounter to watch. The writers presumably know their Marvel comics better than me, and I'm sure they had good reasons to suggest this. Thanos proved himself stronger than any of the individual Avengers, and an encounter like this would have perhaps been the first true challenge for Thanos.
But this scene was never shot. The directors correctly predicted that introducing a new cosmic super-entity at this stage in the franchise would only confuse the audience. Furthermore, it would interrupt the narratives surrounding Thanos and the Avengers that the audience really does care about.
It was a good decision, supported by good advice from Pixar. Even though The Living Tribunal has an established presence in the comics, the movie-going audience was not ready to encounter him. Stories need to be delivered to the audience in the ways that they prefer, not ways that the author might find more accurate, more interesting, or otherwise preferable.