You can't scale the energy a solar panel generates per day from the nameplate capacity because you don't get days of uninterrupted sunlight. It doesn't make much sense to try to estimate at a higher resolution either because of clouds.

Why would you want to do that? And what kind of lighting system in 2026 uses 400 Watts?

A commercial one might and because that's the first step to figuring out how much it uses in a 5 day work week, or per month or year.

Are you seriously saying that when you’re using your 2000 watt hair dryer, you want to pretend that you used it for an hour, and then scale that back to the few seconds you actually used it?

No because if you're measuring usage of something in seconds it isn't going to have a meaningful impact on household consumption.

The reason most people think kWh is intuitive is that they’re used to it because their electrical utility uses it.

Ok even if that is true and they're both equally unintuitive you're the one who wants everyone to switch to an unfamiliar unit for no apparent reason. Why does it make so much more sense to talk about solar and electric car charging on the scale seconds of power than hours that everyone should change units?