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.
As someone who has worked on both sides of the coin in the finance world in consumer credit processing, I think the person you are replying to is more right than wrong, but it's also a matter of how you view the idea of complexity.
I've worked on 30+ year old systems where the code base is absolutely immense, but the <complexity density> of this stuff is very, very low on average compared to the magical bullshit that happens on a simple UI render of some template react app in 2022.
Folks had very little in the way of abstractions at their fingertips, and the languages themselves weren't nearly so helpful in helping you manage complexity, so applications were usually long, shallow, and operating under a litany of fixed boundaries that define and drive a significant amount of behavior for you.
The biggest source of complexity was having to manage your own unique `personal operating system` of bespoke resources at any given time, where each developer was carved into an incomplete walking repository of both business processes and software practices with the passing of each year.
To put it more simply, software can't be more simple in aggregate because we can trivially rely on insanely complex components others have built and made available. Components which were simply not available back then.
Yes, the glue on top might be trivial, but even that frequently isn't.
And if anything breaks down, the humans at the top are normally expected to handle it, no matter where in the stack it is.
I admire what people built with stone tools, but at the end of the day, a modern skyscraper is a marvel of complex engineering with no rival in that world.
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.
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.