You may be taking the wrong conclusions away from most of those scenes. Multiversal theory talks about there being a multitude of different timelines. An infinite number. Timelines that are created whenever any choices is made ever. Which means that there are going to be a hell of a lot of timelines that are functionally identical. (You went to the store for milk on Monday/you went to the store for milk on Tuesday).

Going back in time created alternate timelines the moment the characters arrive. Putting the stones back keeps these newly created splinter timelines from being royally screwed over by the absence of an infinity stone (or three). Each of the four jumps to the past (1970, 2012, space, and Asgard) actually created splinter timelines. Even replacing the stones and Mjolnir is going to leave some differences. Howard's pep talk and the security scare at the compound. Frigga seeing her future son and Jane randomly being put unconscious. Those two are pretty negligible. Tony's heart attack and Loki's dissapearance is going to disrupt that timeline quite a bit. As is the sudden vanishing of Thanos' entire regiment, including Gamora and Nebula. That one's going to go pretty wildly different.