Quote fromThe Legendary weapons, statistically speaking, have never been a great deal different than items of the same iLevel. Better, yes, but not ridiculously. The point of them being Legendary is a powerful proc ability that can literally change how you heal/DPS just by virtue of having it.
Well, Dragonwrath wants a word with you... the procc alone is around 10% DPS increase (the stats increase not even included yet)... or Thunderfury in Classic (which was as good, that in TBC, the first addon after Classic - the best tanking weapon in the first raid instance was still noticably inferior to Thunderfury).
That said, I don't like the idea of Legendaries as done in WoW. I am not one of the people who hate ideas copied from WoW because they come from WoW, but please not THIS particular idea. It is crazy if you have to decide who gets the Caster legendary (for example) if you have several casters who all would qualify the same for it... So I hope they do NOT include Legendaries into SWTOR (or at least only something quite different which only shares the name).