In order to develop the kinds of mental skills you need to tackle complex problems, you need to practice them on simpler problems first (particularly if you happen to be a child). If you decide at a young age it's worthless to attempt any problems that can be solved by a calculator or ChatGPT, you will probably never learn how to solve any problems that you can't use those tools for either.

Also, knowing what kind of things exist and what questions to ask is half the battle. If you haven't stored anything in your head on the grounds that you can outsource knowing things and thinking about them to ChatGPT, you're not going to be able to prompt it efficiently either. It's much harder to sanity check numbers and formulas given to you by others (or ChatGPT) if you can't do any quick mental math. Having original ideas that don't yet exist in LLM datasets also requires storing a lot of concepts and making new connections between them.

I suppose all this is moot if you expect AGI to be available to everyone in the near future, but if it turns out to be decades or more away unfortunately human mental effort will still be required in the meantime.