Do you ever just remember that John Watson is incredibly intelligent?
Like the man is brilliant. He’s an exceedingly accomplished doctor. He’s an army captain (which is not an easy rank to achieve). He’s not just a doctor, he’s a surgeon, a combat surgeon, meaning that he is not only highly intelligent but also responds quickly and accurately under stress. He’s fucking brilliant.
So yeah, Sherlock might be a genius, but John is a genius, too.