I have played HOI3 and been able to build most of the units that the theatre says I need.....
There's your problem, believing the stupid Theater requests. That's a good way to insure a terrible force balance. The AI wants the most expensive of everything, so you end up with a bunch of Strategic Bombers of questionable value that get shot down for lack of Interceptors, and expensive Armor that doesn't have sufficient Infantry to back it up. Building a realistic force balance gave you much better results.
HOI3's biggest issues were with an abysmal tutorial, a manual that quickly became obsolete, tooltips and descriptions which often gave misleading information, and bad publicity from a seriously flawed (almost unplayable) initial release. Aside from that, once it was patched, it was a pretty good game, just a pain to learn because of the documentation issues.
As for education and public knowledge, I overheard one of the local kids explaining US history to his Hispanic neighbor who was hoping to gain US citizenship. The brief summary was to the effect that George Washington started the First World War to free the slaves. It pretty much stopped me cold in my tracks.
That's only marginally worse than the conversation between two piano movers, where the first was unbolting the legs on a grand piano. The second commented about the piano logo, "Kawai? Never heard of them." The first guy: "Brought to you by the same people who brought you Pearl Harbor." The second: "Funny, it doesn't sound German." My expectations on human behavior have subsequently been lowered as a result.