working in the bay area i've never met any software enginer like that, senior or otherwise.
What cities/type of companies to you find "senior" engineers who struggle with basic technical concepts?
What cities/type of companies to you find "senior" engineers who struggle with basic technical concepts?
IME it's much more common in 3rd-tier/mid-market tech companies, or even higher-profile companies where tech isn't the primary operating vertical, and locale != Bay Area.
Companies that can't compete on engineering culture or compensation are naturally going to attract less talented engineers, and there will be a wider variance of skill across the engineering org as a whole.