Earlier quoted context omitted.
The complexity of any software system built in the 70s and 80s is laughably low compared to the biggest system we build today. Their constraints were much harsher, but the fact of the matter is the end result was rather simple by today's standards. I think just the Bluetooth stack in a modern OS contains as much code as an entire Unix kernel from any time up to 1990 or so.
Don't underestimate the complexity of software built in the seventies either for the business, financial or scientific world. We already had virtual machines, HA, realtime and distributed computing back then. Some code running at CERN or NASA was far more complex than a bluetooth stack, yet was also written with teletypes or ADM-3A style terminals.
I'm not saying that NASA or CERN people were dumb or anything, they were probably smarter than the average dev today. But even a genius can only go so far with limited tools.
An elite slinger from the Roman times will probably lose at least 8/10 against a Russian mobilized soldier with 2 weeks of training, armed with an AK-47.
That's how progress works, we both learn ourselves, and more than that, we make powerful and accessible tools.