I may be asking too early, as my Wilhelm is only level 8 in Normal, but it seems he takes a lot more damage - specifically DoT - when hit by fire than my Aurelia character did at the same level. Is he innately weak to fire? I mean, he takes one or two shots from a fire weapon and it’s good night Wilhelm - his life just flies out of him like water out of a broken pipe. Conversely, Aurelia just shrugged it off an didn’t seem to suffer dramatic DoT like Wilhelm seems to.
EDIT: Actually he seems to be weak to elemental damage of any type - just noticed the same thing with other elements; his life just sucks away more noticeably than Aurelia’s (only other character I played so I don’t know about the others).