When you do get the designs you want, you need to dedicate precious factories to building them, and I promise that they're probably all building something else that's war-critical.
At one moment you can be micro-managing a pincer attack on Moscow, controlling one division at a time, and then you can zoom the camera out to encompass a whole hemisphere as you arrange an assault along a front line stretching across all of Africa. Outside those big, pre-war questions of alignment, and who is going to get it in the neck first, Hearts of Iron 4 is primarily a globe-spanning wargame. Here, your options are more stark: as Germany, do you want to attack Russia now or wait until they attack you first? To quote Kierkegaard on the matter, 'Hang yourself or do not hang yourself, you'll regret it either way.' Those are games where the Iroquois can conquer the world, or the Viking can become the militant defenders of the Zoroastrian faith.
It's a very big, very complicated scenario that can play out many, many different ways, but it's not the open-ended playground of Crusader Kings or Europa Universalis. The important distinction between Hearts of Iron 4 and the rest of Paradox's strategy lineup is that Hearts of Iron is a scenario, not a sandbox.
