I too agree that taking both AP Bio with AP Physics in one year just to take AP ES the following year may be unwise. I’m not sure I see the reasoning to take two of the three major AP science classes in one year just to take AP ES (which I think is a good course) the following year. My daughter took all three of those courses but over three years (APES in 10th, Bio in 11th, and Physics in 12th). D loved APES and environmental science was one of her main interests in high school, so the course made sense for her. But even she didn’t see it on the same level as Bio, Physics and Chem.
I think your son can easily not take APES and be fine.