Yah ultimately a parser would just be used by ignorant players to boot people that can't pull their dps up to the level said players want to see. At some stages that makes logical sense but why would SE implement something that would further frustrate players trying to learn their roles and lead to more unsubbers. Makes sense why they don't do it.
That said I like to think that the threat numbers dictate a little of what my damage is on any encounter. Say if during a boss battle I climb to 2 on the threat chart and then pull off to burn adds and then go back to the boss at a 6, and then returning to 2 over the course of a minute or two, I like to think that I'm putting out some solid damage numbers. That's my thought on it anyway