Agreed. With every store stocking every item upon being researched, there is something that feels off.
The idea of different items being in separate stores seems important, to give the game a more "role playing" feel. For instance, one turn after plopping my town down far away from its fellow cities, it can sell legendary armor and create powerful units (limited only by number of citizens). Though it would change the gameplay, I'd like to see a more realistic development to item creation.
Perhaps a town needs certain buildings to build specific items (Ex: leather armor and Metal armor making methods are entirely different). This would allow certain towns to focus on particular objects/ units, as happens in the real world. Doing so would also lead to variety amongst the cities, which currently have few notable differences between them.