On the Star Wars Example:

• The "doomed to fail" rule of the Sith has been averted twice- the Old Sith Empire, and it's successor set up in the Unknown Regions. Both had plenty of infighting as well but both lasted more than a millenium, and functioned relatively well, though that said they were usually not quite as evil as the ones that fell apart. Aside from them, Bane's Sith Order managed to last 1,000 years in secrecy and was still around for a while after the death of Palpatine, if as a shadow of its former self. The other orders lasted long enough to do significant damage to the galaxy at large in each of their turns.

While they last much longer than usual for this trope, Star Wars also has an absurdly long timeline. They all fall in the end, as per the trope. Also, the height of power or damage caused is a non-issue for the trope. It may in fact play into it more often than not, showing how even those Evil Empires that gain significant power will always fall anyway.

I suppose there's an argument for saying that them lasting longer shows that it's an aversion and how they fall may not necessarily fall under the terms of the trope (ie. That their evilness meant it was inherent in the system).

Opinions? Is it too much quibbling on the point? In either direction?