Sure but when you can do a thousand disk I/O operations in less time than it takes to draw to an LCD screen... is the user going to notice that not everything is in RAM?

Apple has been progressively moving things out of RAM and onto the SSD for about ten years now. Try running modern MacOS on a spinning rust hard drive and it's completely unusable these days.

I've been using the same 16GB of RAM on my Mac workstations for the last 10 years and I have more memory headroom every year. Right now I've got two Linux Virtual Machines running on my Mac and I still have so much free memory that 6GB are being used as a filesystem cache (so... a lot of those SSD file reads which would be plenty fast enough, aren't even going to hit the SSD).

If all you do is browse the web... 8GB is plenty. And it also improves battery life - Apple doesn't publish stats but it's common for RAM to draw more power than these laptops can afford with only a 50Wh battery. I'd like to see a test, but I bet upgrading from 8GB to 24GB comes with a considerable real world battery life penalty.

It's too early for third party tests on this model, but the old had the same "up to 18 hours" marketing and third party tests found it lasts between 3 hours playing CPU/GPU intensive games and 30 hours if you really stretch the battery and don't do much (e.g. just read an ebook in a dark room with low screen brightness). You're not going to get anywhere near the highest numbers even under light load with fully upgraded RAM, since it draws quite a bit of power even when it's idle.