Forum:KB:Why are the design flaws the same for Death Star and Starkiller base?

OK so after seeing Rogue One, I have questions as I look ahead.

Looking at the ordeal of what the Empire went through and their efforts to stop the plans from being stolen, why was Death Star 2 and Starkiller Base designed with the same weakness? Sure, there are differences in design and purpose. However, all three are blown up by the thermal oscillator/energy source. How could the Empire/First Order not learn their lessons here?

I am not enough of an expert to answer this but is this is the canon as well? I know Episode VII followed Episode IV but they have now repeated the same mistake two more times.