A proton in a hydrogen atom does not have the same mass as a proton in a Helium atom, nor do any protons in any particular element have the same mass as the protons in any of the other elements. Again, the mass of a proton varies.
Yes, in nucleons of different sizes, the amount of binding energy changes according to quantum mechanics. The result is the average mass per proton is different in different isotopes. The mass differences are explained by the energy differences. Anyway, idk about you, but this really bothers me.
