No, that was the suit
It morphed on the account of it thinking it was human
In the game it was stated that the suit has the potential to transform itself to fit it's user's desires or something like that
At the end of the game, it showed hexagon like panels that where not in place correctly, meaning the suit had changed
Be turned invisible, because of the suit being able to do so
And, yes, he is a shell in a sense
The original user copied his mind into the suit, Alcatraz died, and the suit took over as a result
Ok, I guess I interpreted it as when he killed the alpha Ceph he gained some of its power and during the fall back to earth, his suit burned off. That makes more sense though.
But they are in suits.
Chief specifically in 100lbs of titanium and a superior AI or Prophet in some nanosuit with some piece of shit talking to him that helps in a few places, like being a GPS. Chief has the CE magnum and a SAW.
UNSC titanium is much stronger then ours though, as seen by the fact that the Pillar of Autumn survived falling from orbit, and Spartans can flip/lift tanks.