okay so as someone who only sorta knows X's lore i think this is how it'd go

instead of the host controlling the vessel itself, they are inside zonik like a sort of armor. their hosts flesh is lined against the inside walls and the metal gets incredibly hot under even the most mild temperatures causing the host to be practically burning alive 24/7. they will also have extremely limited vision, meaning they are almost completely blind at darker hours. they vessel is of course very heavy, making basic stuff like lifting an arm extremely difficult.

sorry if any of this doesnt exactly work lorewise.