Every book is different they all have days to avoid. We just go get there early and use your plan. Remember these are averages there is no guarantee that the park will not be crowded that day. We've gone sat went early and have had few problems.
My guidebook says Saturday is a good day to visit when we go in July. I also read that Sunday was a busy day because a lot of Americans arrive on that day and head straight to the Magic Kingdom. I don't know how true this is.
I am just using my guidebook to plan the itinerary and making sure I don't go on any of the early/late entry for Disney guests days which will be busier.