Here are a few more examples of before & after scans of Kirby/Colletta artwork from TwoMorrows new book on Kirby inker Vince Colletta called The Thin Black Line. Vince Colletta: Comics’ Most Controversial Inker, by Robert L. Bryant Jr. The first two scans appear on page 52 of the book, and the third is one of my scans from the published comic book. The art is from Mighty Thor # 152 (May 1968), pg. 4. panels 3 - 4.
The first thing I want to point out is that I don't think that black and white scan is a fair example of the finished artwork. In the published version you can see details such as the lines underneath Thor's eye, so in many respects this comparison is a little unfair to Colletta. I understand the TwoMorrows book is in B/W so printing the published color version is not an option, but I think using the higher-quality color artwork is much more accurate.
But, when we look at the background details we have to ask ourselves: Why did Colletta make those changes to Jack's buildings? Was it because Vince felt Jack's architecture was too complex, and too busy? Did Colletta feel Jack's unique version of NYC wasn't modern enough or aesthetically dynamic? I suspect Colletta made these fairly arbitrary decisions because he was in a hurry -- drawing a very simple checkerboard grid would take much less time than delineating the tiny, intricate details of Jack's cityscape.
Here's a final close-up. You be the judge as to whether you think Colletta eliminated all of those details because he felt Kirby's original pencils were flawed, and his random elimination of details improved Jack's artwork; or do you think aesthetics had nothing to do with Colletta's decision-making and obscuring all of those cosmic circles was done in order to finish inking this page as quickly as possible.