For most people, whats the use case of a laptop?

You only really need one for doing some type of work

OP is trying to say it'll only be a partial replacement.

Ordinary people do everything on smartphones nowadays.

Yeah I can see that. Teenagers are in specially adroit at doing most computer related work from their phone. My niece owns a new Macbook and barely cracks it open. Prefers to do most things on the iPhone and actually manages it.

Me, (old millennial) can not even conceive getting any real work done just on the smartphone. But I'm a power user. I need to log onto linux servers and administer them. Or I need to crack open Excel files and use spreadsheets. Not an ordinary user.

That's exactly the point.

it's gotten to the point where genz doesn't know how to use laptops/desktops

Lots of people don't own laptops or desktops. They do all computing through a smartphone.

Outside of this tech bubble that we are all in, many use them as their primary (or only) computer. More than 60% of internet traffic is from mobile phones.