Agree that having the cores covered is paramount. But the OP’s kid does. And as stated in the original post, kid enjoys STEM. So if he wants to, and can handle, I see no reason not to do both physics and chem. With the caveat that both are a boatload of work.
And while we don’t know the kid’s HS, typically those accounting and general business classes are populated by students not at the high end of the GPA spectrum. The kid already has AP Econ, which is the more important business-type class.
That said, if he wants to take an easy elective, that’s fine too. I highly highly doubt that any college will find fault with whichever schedule he chooses.