Not seeing it doesn't mean you have bad vision(unless you consider 20/15 vision as "bad") Different people see different levels of graininess, some people with excellent vision see none at all.
People seem to forget that almost all of the detail we see is black & white not color. I think the people that are extremely bothered by the pentile pixel structure may have a better ability to localize color than other people. This says nothing about your actual vision.
Another point to consider is that our eyes are great at adapting. The more you use a new screen technology the more "used" to it your eyes will become and the less you will notice things like the pixel structure.