[throwaway1979]

Most systems I've worked with have a core piece that embodies the "hard" algorithm (as you say). The 80-90% of code required to make most user-facing systems work is not "hard" algorithm code in my professional experience. Why does every developer at a company that works on "medical devices, driverless cars, AI / game development, image manipulation, fraud detection, machine learning, data mining, scheduling" need to go through the same interview?

[mgkimsal]

On top of that, I've never interviewed at a company doing that level of complexity where I was going to be expected to write it, from scratch. By the time they're interviewing people, they have something in place, and even if I actually could write it better, politics and personalities are likely going to prevent that anyway (or perhaps even legal).

More than likely you'll be working on a team, where you need to understand some of these concepts, and you'll grow in to them. Almost every single person on that team did not come in off the street with expert knowledge in those domains.