That's a logical interpretation, but according to the Visual Dictionary, the Sith Destroyers were, in fact,
a different design that was almost twice the size of an ISD-1 despite looking perfectly identical, down to the relative size and placement of the windows (I guess the officers on the bridge probably got a little step-stool so they could see out the viewport).
Still, Rose's line about researching old Destroyers, the color of the Sith TIE Fighters, and the fact that the ships looked exactly like Early Empire/Extremely Late Republic-era ships suggests they're an older generation of technology. Potentially predating the Death Stars, definitely predating Starkiller Base. How much further will it go? In a thousand years, will every fighter and smuggling freighter have a planet-cracking laser on it? Will there be a hand-held version?