I'd like you to understand what youre asking:

If you properly scale the potency of the skills, which is what I believe youre asking, to make it fair to everyone else so that you're not one-two-slapping the boss. By the time you've done your level 90 rotation and tossed out your oGCDs... the boss will already be dead, or close to it. At level 50, bosses die within 1 minute, maybe a little more. You will have done your beginning burst, and gotten halfway through to your 2 minute rotation. In comparison, at level 90 dungeon bosses take roughly 3-4 minutes. Enough for your beginning burst, your 2 minute "rotation", and your second burst.

In order for you, as the level 90, to single-target kill something at level 50, it will take (for example on drg), the same time as it does to kill a level 90 mob... when it takes a level 50 player less than half that time. Again, this is in the hypothetical scenario that all potencies have been properly adjusted to account for fairness in potencies.