"GD is new"
yes, it was introduced more recently than the steam engine. I first used it in ~2005. The idea of reinforcing the red bits and getting rid of the blue bits is older than that.
Agree, it has come into its own with 3D printing. Of course now all you need to know is what the loads are!
I think by AI you probably mean a genetic algorithm, I wrote that in Matlab to optimise a ladder frame chassis a couple of years later after playing around in Optistruct. At the time commercial structural optimisers didn't use beam elements, they do now. Basically - here's the hardpoints that need to be connected. Here are the loads at those points (I may have just used torsional stiffness). Here are the available section sizes. Use the best combination of section sizes to get a light stiff structure. This was for a 55 Tbird, it was quite interesting how hard it was to practically improve on the efficiency of the original design (stiffness/mass), the main mod I made was to add a X brace at the kick-up for the rear axle.