What you guys are talking about is largely irrelevant becuase it´s likely you won´t be much better than your opponent at that role.
Raising ELO isn´t about carrying it is about improving and being a positive influence on your team (which includes not flaming and being nice). Most people don´t like jungling and supporting hence they are the easiest roles to outplay your enemy in, meaning they are probablly the best for raising ELO with.