One of the smartest people I know and one of my best friends has aphantasia and no voice in his head, but got perfect scores on calculus and engineering exams, even those for which I had to visualize the forms and calculate based on that. Like multivariable calculus is all about 3D and eventually all other D shit and he got perfect scores with no concept of imagining the shapes. We discuss this a lot generally, because he still works in a research field that I can only grasp visually and he has absolutely no ability to do so but understands it better. He also reads so fuckin fast because he doesn't have to wait for the voice