In World War I, German Jewish scientists contributed to the German war effort. In World War II, refugee scientist contributed to the Allied war effort. Tyrants can shoot themselves in the foot quite effectively.

A few top physicists were left in Germany, including Heisenberg, but it was not enough to move the project forward, and it's suspected that Heisenberg may have deliberately sabotaged the project.

But you have a point. So long as AGI is at the cutting edge, only a handful of top people can move it forward. As Moore's Law of Mad Science has its effect, "ordinary" scientists will be enough.

(And to make it clear, I am not suggesting that the US government is tyrannical.)