And the GE is arguably the 2nd most succesful Empire ever. They destoryed the Republic which has never been done before and destroyed ALL of the JEDI. Who cares how long it lasted, they achieved the almighty goal.
And the Jedi dont? in folowing your reason even the jedi were more sucessfull. In destroying the sith empire.... uh how manny time sexactly 2 or 3 or more i just lost count.
My take on this issue is light and dark will always be there as well the fight against the darkside. always.