I think it still makes sense. It takes much longer to design and build a prototype. How long would it take to design the first working automobile vs. building a second one? They probably had to build tools and figure out numerous issues that could easily be bypassed in the construction of the second one. They did build in different locations and it sounds like construction near Endor offered a much closer supply of raw materials.
I'm sticking with my theory that the super laser was the big delay on the first DS as well. In the novel about the DS, they talk about the need to test it on a prison planet, which suggests this was the last part of the station to be built. The second time around, they could rebuild or even enhance the laser with much less effort. The physical construction of the shell of the DS maybe takes 4-5 years, hence the Laser being operational, but the full sphere/interior not yet being completed in ROTJ.