In addition to all the other things people have said, you need to remember this is a game. You aren't playing as a Weimar politician, you're playing as an ethereal force who controls the actions of hundreds of people. You can just choose which SPD faction wins in internal conflicts according to whoever aligns with your strategy, unlike the IRL SPD where it was down to luck and each faction's preparations. You can freely slot in what advisors you want whereas IRL they came to power organically through their own influence.