The Death Star was always a bad design. You have to wonder how many of Palpatine’s cronies were in on it for the graft (and if any of them survived...).
The Death Star required massive resources to construct, yet it can only be at one place at a time. A large fleet would be a better investment since, when necessary, can be massed to produce near equal result (rendering a planet uninhabitable by massed bombardment) or to gain space superiority over an enemy fleet, then dispersed again to cover many, many potential trouble points with squadrons of Star Destroyers.
Sort of like Hitler blowing precious resources on his V weapons and Saddam on his super-gun the Israelis could of taken out with a few guided weapons.