I don't really see how this would make jobs more "interesting" or add any element of strategy. It seems like it would just be the game telling you what jobs to play for what content. Imagine queuing in Duty Finder for a roulette, and you find out all your damage is resisted by the boss. Okay...? There's nothing you can do about that, so how does that change your strategy at all? You just play the same way, but get punished with a slower fight. Or conversely, if you lucked out and picked the "right" job, you get arbitrarily rewarded for nothing. Not to mention, the risk of the "wrong" DPS getting kicked from the group.

Even that idea you described, where a magical DPS can apply a buff to a physical fighter and mitigate the penalty... so, they do that, and then what? They just do the fight as normal? Seems like we didn't really add anything of substance. Help me out if I am missing something or not understanding what is being asked for.