OTOH, I actually have an engineering degree and I can't build a bridge, a radio, or a robot, despite having looked at all those things during the course.

People who can actually do it have done it for a lab or a business, and then get accredited.

My impression of the engineering degree is that it's basically a certificate in being able to deep dive into... something. Whether that's actual bridges or financial derivatives or trading systems, a degree basically says you haven't given up on some large pile of math-heavy topics, so an employer should bet on you being able to learn their thing. It's also the case that there isn't enough time to learn a whole business, so really it's testing that you stuck with the introductory parts of a wide variety of techie things.