You know that images lose quality when you scale them up, right? You should NEVER compare things like this by scaling them. Always keep things to their original resolution.
And again, there'd be no cuts like that ANYWHERE because THAT'S NOT HOW THE MURAL WORKS. Every character is their OWN LAYER. If Isaac was scheduled and had to be swapped for Isabelle, it would have NO EFFECT on Olimar or Bowser. It would just be a matter of turning Isaac's layer off, Isabelle's layer on and moving the other characters. There'd be no "crop" at all.
Okay, sorry for scaling it up, certain people were claiming that they couldn't see the cut. You can go check it out for yourself though, it's there.
And clearly, you don't get how the mural works. It's cut into separate images. That seam is the seam between images. What happened was this:
8-8 direct Olimar Image - Cloud Image
Lined up perfectly
September direct Old Olimar Image from 8-8 - Isabelle Image
There was a crop
Few days later New Olimar Image to fix the crop - Isabelle Image
Fixes most of the crop issues, except for the fact that Olimar only shows on the left side of the cut, not the right. This proves he wasn't intended to be there when the Isabelle image was created. Clearly, the segments were saved at different times.