I think Anbokr was going for the illusion thing, but I don't agree with it. Spectre illusions are fundamentally different. They can't be controlled, and are on a long cooldown, can't be used for farming, and due to their auto AI it isn't that hard to tell which is the real one in a fight.
Spectre is a beast due to her Global presence and great late game damage mitigation. Naga and TB both have access to using their illusions to farm, and each has their own respective team fight ability, song having wonderful engagement/disengagement properties, and Metamorphas and Sunder making Terrorblade a man fighting tower killing monster.