The Empire knows where to pull their strings economically, unlike the Republic. The Empire has always obtained the greater fleets and army size, its because they have the bigger resources and economic power. In fact, the Republic was almost destroyed because the Mandalorians (secretly working for the Empire) performed a blockade. This almost made the Republic force surrender UNDER ECONOMIC PURPOSES.
Lets not forget that the 2nd half of Kaas is entirely under construction. No really, one area is the site of a huge monument and resources while the other is the start of a complete expansion. Even the NPCs state that they are expanding at an alarming rate.
The Empire takes their resources while the Republic tries to negotiate for them. This is what makes the Empire stronger economically. Shame that their lust of power often creates shattering betrayals.
Which is why an Empire without the Sith would be a powerful force to be reckoned with.