It’s not the worst advice to try hard things

No, absolutely not. I agree.
But framing it as if going after hard problems is all you need to succeed is disingenuous.

As far as I understand it, gen z's primary issue is that outside factors, those beyond "running towards the hardest problems" and outside of your direct control are stacked against them, whereas it used to be more favorable according to them.

Whether that perception is correct or not, telling them to just "do harder things, stupid" has close to zero value from that perspective.