When someone is fixing it in postprod most of complexity of the initial shot is gone never to be seen again. It is not like they fix some colors on the scene and then last scene of the movie suddenly changes to something different :D
Have you seen the amount of changes George Lucas did when editing the prequel trilogy of Star Wars? They were digitally composing individual actor performances within a shot.
Isn't Lucas known for being an outlier in the industry in his devotion to post-production editing? I honestly don't know. But I am unsure that other production teams are capable of pulling this off and shipping on schedule with the same aptitude.
I've also heard this practice blamed for enabling a decade of "bad cgi"—visuals are reworked and reworked until time runs out, and in a rush they ship visuals that are worse than in movies 20 years ago. Explicitly: it's not the artist, it's a production pipeline failure. And indeed, it's easy finding marvel movies whose CGI looks closer to that of a video game than Lucas's prequels. Heck, even the sequel movies fall into this category.
