Let see If person born with power is called X and a person is given a power is Y, then you could get XX, XY, YY, or YX, so the question now coes down to who falls into which group.
XX - Rare power by birth - Peter, Sylar
XY - Normal Power by birth - Adam, Matt, Heiro, Pa Petrelli, Matt's father
YX - Artifical power at birth (normal) - Nathan, Tracy
YX - Artifical power at birth (defective) - Claire, Elle
I'm not sure I follow you here. How do you intend this to be read? Unless you intended the (defective) line to be YY, and trying to imply that maybe Meredith is also an artificial. But Bob (Elle's father), is in all likelihood a natural (being one of the Company founders), so the would have to move Elle up at least one "notch" on your scale.
I'm of the opinion that Claire and Elle's powers are not "defective" though, merely evolving... just not in an immediately enjoyable/beneficial way. There was an implication, at least with Parkman, that powers could grow over time and with use, and by tying the in with Ted Sprague, are not always entirely controllable.