In my experience the speed gains are real (kind of) but not in a "the AI writes code" kind of way, more of a "the AI is Google on steroids that can reference the docs very quickly". I've found it saves me a ton of time searching through documentation, googling and dealing with bad search results or ads, etc... But it doesn't write good code. So a productivity boost, not 10x, but a bit. And no, I wouldn't fire anyone. It's not that good.