>>81584874they are both physical conduits of power.
others merely manipulate various powers with their mind. They can do that, but also they can suffuse the energy through their whole body, and they can possess limitless energy.
It was said that the reason scott needs a visor is a psychological block, and i think it was implied at some point that Sinister might have done something else to limit him, but that plot point never came to fruition. Without that block he'd be like vulcan but more powerful.
Essentially they can absorb store and manipulate limitless amounts of energy and enhance their own bodies with it.
Also at the time mutants didn't have a gene called X that gave them powers, but had different mutations which gave different powers. In fact in Genosha they changed mutations to give people different powers according to what type of slaves they needed.
scott and jean had very powerful and stable mutations
