Demonstrably bad at research and math, yes. So don't use them for that purpose. A lot of work is being put into this area though, so it might change in the future.

Basic writing? That's such a broad task. As evaluated by what metric? One thing they're very good at is writing texts that sound like they're written by a human. If that's what you need, then they're great for the task. Especially so if you need a lot of it. I wouldn't say that the ability to write a thousand words per minute is a foundational skill for anyone.