b.)DD With his vision problem
And he has extra senses that enable him to see in radar vision...
a.)charles with his incapability to walk yet his works are on a global scale, and the fact that he will never be fully accepted without prejudice but keeps on fighting for them
Lot of crippled people have business and stuff...and all the X-Men keep fighting for the humans too...
All of them have courage and willpower in spades, or else they wouldn't be superheroes. All of them have stepped up to the plate and faced seemingly inconquerable odds. All of them have stared death in the face.
I think the point is that even with these disabilities, DD and X excel, while Cap and Sue have no such restrictions.
I'd say top wills in Marvel are Doom and Strange.
Long already showed why Strange is top tier, so I'll show why Doom is.
Doom (with Galactus' power), in his battle against the Beyonder got his leg torn clean off. He then used an astral projection to ask for help from the heroes. They told him to screw off, so he said "F*** it, I'll do it by myself!!".
Doom continued the fight and quickly lost another limb (his arm). He had lost two limbs, and was getting his ass handed to him on a silver platter, but he STILL kept fighting!! Beyonder got tired of slapping him around and started dissecting his body. Doom (almost half dead) shut out the pain and used his big noggin combined with Galactus' cosmic might to lay Beyonder out flat.
He lost an arm and a leg AND half his body was being dissected but Doom kept coming--and defeated an "unbeatable" foe. If that aint willpower I don't know what is...
"No one rivals Doom! There is no power on Earth, no intellect in all creation, to equal mine!!"