Not to be all blurf about this but Peter Arthur and Sylar all have the same power. Also I imagine these writers only did what they did to Peter in order to candor to the way the audience felt that super powered characters like him suck. If they intended for his power to have always been like that I would be amazingly surprised.

Apparently their power of empathic mimicry is dependant about their personality. Sylar apparently has his manifest as eating brains (j/k), Peter used to have it as simply knowing people meanwhile Arthur just steals it.

Sylar once was able to use his powers the same way Peter used to be able to, but then was like no thanks.

If this new power is the same power he always had then it might be his personality that is affecting it.

Or it could simply be a power like matts where you have to have your power evolve over time. I think matt used to only be able to read minds, then one day blam he could control people.