It's definitely an objective phenomenon but there's two factors at play: first is the monitor quality. I have two monitors of the same model number but made in different years with obviously different panels (color reproduction is all over the place between them), and the banding is obvious in one monitor but not the other. I can drag the window between screens and it disappears. On my iPhone, it's very obvious.

Second is how much each person's brain interpolates. I got used to those visual artifacts on the web in the early 90s so my brain started doing its own interpolation. It took reading the entire article and flipping tabs back and forth to compare images before I noticed the difference. Now I can't unsee it in other images that I recently converted to webp for a project.