We don't have any such understanding, or even a definition, of 'AGI'.
Leo Szilard had more plausible philosophical musings in the early thirties, that did not have root in any workable practical idea. The published theoretical breakthroughs you mention didn’t happen until the late thirties. Nuclear fission, the precursor to the idea of an exponential chain reaction, happened only in 1938, 7 years before Trinity.
He didn't have internal combustion engines, but that's a practicality, other mechanical power sources already existed (Alexander the Great had torsion siege engines). They would never be sufficient for flight, of course, but the principle was understood.
But he could never have even begun to build airfoils, because he didn't have even an inkling of proto-aerodynamics. He saw that birds exist, so he drew a machine with wings that flapped. Look at the wings he drew: https://www.leonardodavinci.net/flyingmachine.jsp
That's an imitation of birds with no understanding behind it. That's the state of strong AI today: we see that humans exist, so we create imitations of human brains, with no understanding behind them.
That lead to machine learning, and after 40 years of research we figured out that if you feed it terabytes of training data, it can actually be "unreasonably effective", which is impressive! How many pictures of giraffes did you have to see before you could instantly recognize them, though? One, probably? Human cognition is clearly qualitatively different.
The danger of machine learning is not that it could lead to strong AI. It's that it is already leading to pervasive surveillance and misinformation. (idlewords is pretty critical of OpenAI, but I actually credit OpenAI with taking this quite seriously, unlike MIRI.)
Nuclear weapons required enriched uranium, and the gaseous diffusion process of the time was insanely power-hungry. Like non-negligable (>1% ?) percentage of the US's entire electrical generation power-hungry.
This is what happened when it became known nuclear weapons were a viable concept. The technology shifted power to such an extreme degree that it was impossible not to invest in it, and the delay from «likely impossible» to «done» happened too fast for most observers to notice.