What about the ability to "shroud" the powers of others?
I mean, sure, the ability to "hide from other force sensitives" seems to have been learned by the Jedi finally in the OT era, but still. The above seems to be a unique power the Sith have.
The two powers together seem to be what Lucas was citing as proof that the Dark Side was stronger (in his AOTC commentary).
I wonder if he clarifies this or contradicts himself in the ROTS commentary? (I still don't have it yet)