So here's a thought...the First Order's Death Star-Essie weapon seems poorly conceived.
The neat thing about the Death Star was that it was mobile...it could move around the galaxy as necessary to attack its targets.
Does the First Order's weapon do that? It seems to me like it's a planet locked in orbit.
I think as long as they eliminated the Republic, that wasn't a concern. The Death Star was intended to be this watchdog over the galaxy. For the few uses they made of Starkiller Base, it seems like it would've completely wiped out all opposition.