> even seemingly "senior-level" people (people with years of programming "experience" on their resume) have shown an inability to do basic coding from scratch.

I wouldn't have believed you a few months ago (and your statement is still stronger than my experience), but I've finally seen people who are so maintenance-bound, that even though they're good at _that_, they've never managed to learn the language (the corners, idioms, and semantics) they've been maintaining. It's probably a sign of heroism that they picked up enough to do so on the fly, but, you wouldn't hire them to write new code.