I think people are overstating the difference between a major in any subfield of biology vs. biology. You can usually major in biology and focus on a particular area anyway. Certainly at the PhD level there’s a feeling that someone with a PhD in neuroscience can’t just jump in and do immunology work the way a PhD in immunology could, but at the undergrad level the differences in the depths between a major in biochemistry vs. biology vs. neuroscience vs. immunology isn’t that much. Especially given the type of work you’d be getting hired for anyway.