couldn't a void player technically kind of... do the opposite of their class? or specifically NOT do that? they might 'create nothing' or 'destroy nothing' or 'steal nothing' or 'change nothing' right? then they could essentially have a role that revolves around AVOIDING the specific behaviour their class would normally be associated with?

In some cases? But not always. For example, Horuss had Nothing served to him, so unlike most Pages, he didn’t have help backing him and he had to build himself up from nothing. Even then though, look at Roxy, she’s very Roguish. So it’d be a case by case basis, and not with all Classes.