"None of the interviews asked about my ability to design systems, how to test or manage large-scale applications, how to gather requirements and work with customers."

No company will ever ask such questions, which is mind boggling. They will all ask minute questions about sorting algorithms which you will never code instead of asking questions related what you will be doing day to day or stuff that is actually critically important.

No one asks design questions, perhaps because it is an open-ended question. But aren't those the best question for a role that often requires coming up with new solutions?

EDIT: perhaps I was too harsh by saying "never". In my experience, companies have occasionally asked about design, but very few and very little in terms of the ratio with algorithm questions. Part of the problem is the "new interviewer every 45/60 minutes" style of interviewing. They all come in and start off with an algorithm question. Each and every one (at least the technical ones).