Capable of it or capable of learning it when it's needed? I had to brush up on linear algebra for some problems at work about 2 years ago. I solved the problem, documented everything properly, and the code has been running unchanged and without issue ever since. In the time between then and now I've definitely lost that knowledge _yet again_.

Sure, but it doesn’t matter enough that interviews should be built around this domain, especially to the extent they are around the Bay Area.

Having 0.5% of all engineers regularly engaged in working with the implementation details of data structures and algorithms does not justify putting 100% of engineering candidates through interviews centered on that topic.