I'm sorry, but your statement:
Thirty years ago, the idea of NP-completeness had not been invented. Nobody had the slightest idea that some problems were intrinsically hard. Nobody had even seriously thought that it might be possible for a problem to be intrinsically hard.
Is just plain wrong. P/NP discussion is almost 100 years old and comes out of Mathematical Logic. The halting problem is older then computers... unless you count a Turing Machine.
Church, Turing, Hilbert, Frege, Goedel... those guys were working on this stuff when light bulbs were still a novel idea.