I think you're missing the fact that using these skills out of their native class does reduce the skills effectiveness, and does remove some of the bonuses associated with them, magic being the most prevelant, as you cannot aoe on a DoW using magic.

Even with extra affinity, the effectiveness is still reduced, which means you choose the skills you find useful to you, and make yourself unique, a unique gameplay style. Are there thousands of others who had the same ideas as you as to what skills to use? probably, it doesn't take much to figure out what works.

Like i said, you've structured this well, but i wonder if you've actually checked on how the skills work already for yourself before coming to these conclusions, or went off of what someone else told you.