The short answer is yes. A child can be gifted in Math and not in English or vice versa but this usually aligns with a MG child. Then you get into how advanced is a MG child in their area of advancement? Most will do fine with AP classes at their respected grade level.

As for HG+ children, someone correct me if I'm wrong but I understand they are advanced in all areas. They might be stronger in a specific subject because they are more passionate about the subject but overall they are advanced.