You guys are making this more complicated than it needs to be. Jobs have set roles, specific roles, even the game acknowledges that.

You don't pick a healer if you want to DPS, you don't pick a tank if you want to heal, and you don't pick a DD if you want to tank. Simple as that. To expect more from anyone, even if you and everyone else around you think that's how things should be done, is selfish and does more to hurt the groups they're in than any "wasted" time. Really, most of what you're doing is trying to impose dangerous habits that may not actually work for future content. Why needlessly make things more difficult and tedious for those just making it to end-game? The logic should always be for players to assume their roles and nothing else -- unless they're comfortable with taking on additional responsibility and the group isn't being put in any unnecessary situations because of it.