Frontend devs can do many tasks that systems engineers (who can supposedly whip out algorithms in their sleep) cannot do: - Make pages render properly in all popular browsers - Make responsive UIs - Align text of variable length in the vertical center of a page - Know when to use tables and when not to - Understand when to use a SPA app and what not to - Make SEO friendly pages
etc.
All this has nothing to do with said algos. I really think that people who don't understand this should not be interviewing frontend engineers.