It WAS practical though. You are forgetting how messy sociology is. By making a "boogeyman" out of Jews and others, the Nazis legitimized their regime. And not only that, they scared the populous into granting them power because "otherwise the Jews will get you."
It might not seem very practical or efficient because you lose assets like Einstein. But having assets among your intelligentsia is only one practical matter among many that a fledgling regime must consider. A blindly obedient populous might also be counted as an asset.
Therefore, human rights are not a practical matter but a moral matter. Under certain conditions, tyranny works. And sometimes it works pretty damn well.
You make some good points, although I would still maintain that, in the long run, their policies brought about their own failure - mainly because they went too far, alienated so many people, operated without any semblance of restraint or honor - and ended up angering more and more people who wanted to wipe the entire country off the map.
So, yes, tyranny did work, to a point - and I would concede that nationalism, in and of itself, can be quite compelling, especially for a nation like Germany still reeling from their defeat in WW1. Plus, they felt threatened by the rise of the Soviets and their own Communist Party in Germany, so it seems that many Germans probably didn't care so much about "rights" as much as they wanted a strong leadership to protect them from enemies and to restore their national honor. It might be argued that, since they had been used to living under Kaisers and the iron-fisted rule of men like Bismarck, it was something more familiar to them, so their political culture wasn't really geared towards that concept. But after WW2, Germany and the world ended up learning some harsh lessons.
I agree that human rights are most definitely a moral matter, without question. However, there is still a practical side, since the general focus of public opinion also tends to carry a certain of moral and social consciousness. It's not like in the past where the political culture tended to think it was okay to have segregation or deny certain groups rights - or in some regions or countries where the population was largely kept ignorant so they weren't even aware that they had rights. Now, more and more people are literate and aware of the world. (Dare I say "woke"?) People are aware that they have rights as citizens and as human beings, so tyranny is not as easy to maintain as it used to be. It's still easy to scare people and make them afraid of bullies, but there are more places for people to run these days - and a plethora of media for people to tell their stories of tyranny to the world. And the world can and does react - sometimes, but not always.
So, even tyrants of today have to "play the game," so to speak, to try to make it look like they're supporting human rights and legitimate legal principles.
